untitled

Atari*

System Reference manual

Bob Duhamel

6915 Casselberry Way

San Diego, CA 92119

*Atari is a registered trademark of Atari Corp.

This manual contains highly technical information. Such information

is provided for those who know how to use it. To understand the

advanced information you are expected to know 6502 assembly language.

If you are new to programming, concentrate on the parts which discuss

BASIC commands.

Addresses are usually given in both hexadecimal and decimal numbers.

The operating system equate names are given in capital letters with

the address following in brackets. The decimal address is in

parenthsis within the brackets. For example:

DOSVEC [$000A,2 (10)]

name hex dec

The ",2" after the hexadecimal number means that this address requires

two bytes to hold its' information. Any address called a "vector"

uses two bytes whether noted or not.

Control registers and some other bytes of memory are shown in the

following format

7 6 5 4 3 2 1 0

-----------------

| |

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

The numbers on top are the bit numbers. Bit 7 is the Most Significant

Bit (MSB) and bit 0 is the Least Significant bit (LSB). The numbers

on the bottom are the bit weights. These are useful when changing

memory with decimal numbers, as you would in BASIC. For example, to

set bit 4 of a register to 1, without changing any other bits you

would add 16 to the decimal number already in the register. To reset

the same bit to 0, you would subtract 16 from the number in the

sets bits 3 and 4 of a graphics mode control register.

MSB and LSB may also mean Most Significant Byte or Least Significant

Byte, depending on context.

THE CENTRAL INPUT/OUTPUT UTILITY, (CIO)

The ATARI computer uses a very easy-to-use input and output

system called the Central Input/Output utility, or CIO. Nearly all

input or output passes through this utility.

CIO uses eight "channels" as paths for I/O. There are not really

separate channels for I/O but the computer acts as if there were.

Each channel is controlled by a 16 byte block of memory called an

Input/Output Control Block or IOCB. The channels are used by putting

the proper numbers in the proper IOCB bytes then jumping to the CIO

routine. In BASIC, complete I/O operations can be as easy as typing a

command such as LPRINT. In this case BASIC does all the work for

you.

THE CIO CHANNELS

There are eight CIO channels, numbered from 0 to 7. In BASIC some

channels are reserved for BASIC's use.

BASIC CIO channel assignments

Channel 0 Permanently assigned to the screen editor

6 Used for graphics commands

7 Used for the Cassette, disk and printer

Channels 6 and 7 are free to use when they are not being used by

BASIC. With machine language, all of the channels are available to

the programmer.

THE IOCB STRUCTURE

The IOCB for channel zero starts at address $0340 (decimal 832). This

is the only address you need to know. Indexing from this address is

used to find all of the other bytes. Below are the names and uses of

the IOCB bytes.

IOCB bytes and uses:

ADDRESS NAME EXPLANATION

$0340 ICHID handler Identifier

$0341 ICDNO device number (disk)

$0342 ICCOM command

$0343 ICSTA status

$0344 ICBAL buffer address (low byte)

$0345 ICBAH buffer address (high byte)

$0346 ICPTL address of put byte

$0347 ICPTH routine (used by BASIC)

$0348 ICBLL buffer length (low byte)

$0349 ICBLH buffer length (high byte)

$034A ICAX1 auxiliary information

$034B ICAX2 -

$034C ICAX3 the remaining auxiliary

$034D ICAX4 bytes are rarely used

$034E ICAX5 -

$034F ICAX6 -

ICHID

When a channel is open, the handler I.D. contains an index to the

handler table. The handler table (to be discussed later) holds the

address of the device handling routines. When the channel is closed

ICHID contains $FF.

ICDNO

The device number is used to distinguish between multiple devices with

the same name, such as disk drives.

ICCOM

The command byte tells CIO what operation to perform.

CIO command codes

HEX DEC

+Open $03 3

+close $0C 12

get $07 7

put $09 11

input $05 5

print $09 9

+status

request $0D 13

+*special >$0D >13

+ command may be made to a closed channel

* device specific commands

ICSTA

The status byte contains an error code if something goes wrong. If

bit 7 is 0 there have been no errors.

ICBAL and ICBAH

Before a channel is opened, the buffer address bytes are set point to

the block of memory which contains the name of the device the channel

is to be opened to. Before actual input or output these bytes are set

to point to the block of memory where the I/O data is stored or is to

be stored.

ICPTL and ICPTH

The put routine pointer is set by CIO to point to the handlers'

put-byte routine. When the channel is closed the pointer points to

the IOCB-closed routine. This pointer is only used by BASIC.

ICBLL and ICBLH

The buffer length bytes show the number of bytes in the block of

memory used to store the input or output data. (See ICBAL and ICBAH.)

If the amount of data read during an input operation is less than the

length of the buffer, the number of bytes actually read will be put in

ICBLL and ICBLH by CIO.

ICAX1 through ICAX6

The auxiliary information bytes are used to give CIO or the device any

special information needed.

OPENNING A CIO CHANNEL

Before using a CIO channel it must be assigned to an I/O device. In

machine language you start by putting the channel number in the four

high bits of the 6502 X register (X = $30 for channel three). Next

you place the necessary codes (parameters) into IOCB 0 indexed by X.

The X register will cause the numbers to be offset in memory by 16

times the channel number. This puts the numbers into the correct IOCB

instead of IOCB 0. Below are the parameters used to open a channel.

Channel-open parameters:

ICCOM open code

ICBAL address of device name

ICBAH in memory

ICAX1 direction code

ICAX2 zero

The direction code byte in ICAX1 takes on the following format:

ICAX1 format for opening a channel

7 6 5 4 3 2 1 0

-----------------

ICAX1 | W R |

-----------------

8 4 2 1

W 1 = open for output (write)

R 1 = open for input (read)

ICAX1 may have the following data

CIO direction codes

HEX DEC operation

$04 4 input

$08 8 output

$0C 12 input and output (cannot change the length

of a disk file)

ICBAL and ICBAH point to the device name stored in memory. The device

and file name must be followed by 0 or $9B (decimal 155).

Once the parameters are set, jumping (JSR) to the CIO vector

(CIOV) at address $E456 (58454) will cause the channel to be opened.

In the following example a basic knowledge of assembly language is

assumed.

Routine to open channel 1 to the keyboard:

ICHID = $0340

ICCOM = ICHID+2

ICAX1 = ICHID+10

ICAX2 = ICHID+11

IOCB1 = $10 channel in four high bits

CIOV = $E456

OPEN = $03

OREAD = $04 ;open for input

ERROR = (address of error handling routine)

;

START LDX IOCB1

LDA OPEN

STA ICCOM,X

LDA <NAME

STA ICBAL,X

LDA >NAME

STA ICBAH,X

LDA OREAD

STA ICAX1,X

LDA #0

STA ICAX2,X

JSR CIOV

BPL OK

JMP ERROR

;

NAME .BYTE "K:",$9B

OK (program continues here)

To open a CIO channel in BASIC the OPEN command is used.

BASIC OPEN command format:

OPEN #channel,aux1,aux2,device:file name

aux1 = direction code

aux2 = special code

To open channel 1 to the keyboard in BASIC Type:

OPEN #1,4,0,"K:"

The third parameter, aux2, is a rarely used special parameter. One

use is to keep the screen from erasing when changing graphics modes.

The fourth parameter is the device to open the channel to. It may be

either a string in quotes or a string variable.

CIO device names

C cassette recorder

*D disk drive

E screen editor

K Keyboard

P printer

*R RS 232 I/O port

S screen handler

* Uses a non-resident handler loaded by the device at

power-up.

The device name must usually be followed by a colon. With the disk

drive a file name is expected after the device name. The screen

handler is used for graphics. The screen editor uses both the

keyboard handler and the screen handler to work between the keyboard

and screen.

USING AN OPEN CHANNEL

Once a channel is opened to a device you have several options:

INPUT: (ICCOM = $05)

The computer reads data from the device until a carriage-return is

read (decimal number 155, hex $9B) or the end of the file (EOF) is

reached. A carriage return is also known as an End-Of-Line or EOL.

The IOCB input parameters are:

IOCB input parameters:

ICCOM get record code

ICBAL address of buffer to

ICBAH store the data in

ICBLL length of the data

ICALH buffer

The following routine demonstrates the input command in assembly

language. Some of the equates are in the channel openning example

above.

Input routine:

GETREC = $05

BUFF = (address to store data at)

BUFLEN = (number of bytes available at storage address)

LDX IOCB1

LDA GETREC

STA ICCOM,X

LDA < BUFF

STA ICBAL,X

LDA > BUFF

STA ICBAH,X

LDA < BUFLEN

STA ICBLL,X

LDA > BUFLEN

STA ICBLH,X

JSR CIOV

BPL OK2

JMP ERROR

OK2 (continues if no errors)

If the data retrieved is shorter than the prepared buffer, the number

of bytes actually read will be put into ICBLL and ICBLH.

In BASIC, the INPUT command is used.

BASIC INPUT command format:

INPUT #channel,string variable

INPUT #channel,arithmetic variable

For example:

INPUT #1,IN$

The above commands will cause the data from the device to be put into

the specified buffer (IN$ in the BASIC example) until an EOL is

reached. If the INPUT statement is used again, without closing the

channel, the computer will get more data from the device until another

EOL is read or the end of the file is reached. The new data will

write over the old data in the input string or buffer. If an

arithmetic variable is used, only numbers can be input.

PRINT: (ICCOM = $09)

In assembly language the print command is identical to the input

command. The only difference is that the PUTREC code ($09) is stored

in ICCOM. Of course the buffer bytes of the IOCB then specify the

block of memory to be output from rather than input to. With the

print command, EOLs within the string or buffer are ignored but an EOL

is placed at the end of the data when sent to the device.

In BASIC, the PRINT command is used like INPUT except you want to use

a semicolon instead of a comma to separate parameters. For example:

PRINT #1;OUT$

PRINT #1;"HELLO"

If you use a comma, ten space characters will be sent before the

string.

If the print command is used again, without closing the channel, the

new data will be appended to the end of the data previously sent. Old

data will not be written over.

GET: (ICCOM = $07)

In BASIC this command inputs a single byte of data from the device.

EOLs are ignored. In BASIC, GET is used like INPUT except an

arithmetic variable must be used. For example:

GET #1,IN

If the get command is used again the next byte from the device will be

read. If the end of a file is reached an error will occur.

There is no command in BASIC to input an entire file without stopping

at each EOL. If you wish to ignore EOLs while reading a file to a

string, you must use the GET command. Each byte of data is then put

into the string by the program.

EXAMPLE:

10 OPEN #1,4,0,"D:TEST"

20 TRAP 60:REM GOES TO LINE 60 WHEN END OF FILE ERROR OCCURS

30 GET #1,IN

40 IN$(LEN(IN$)+1)=CHR$(IN)

50 GOTO 30

60 CLOSE #1

In assembly language, the get command can be used to get any number of

bytes from the device. It works just as INPUT does except EOLs are

ignored.

IOCB get-byte parameters:

ICCOM get-character (single byte) code

ICBAL \

ICBAH same as in input

ICBLL

ICBAH /

Other than the ICCOM code (GETCHR = $07) this command is identical to

the input command.

PUT: (ICCOM = $0B)

In BASIC, PUT is the opposite of GET. It outputs a single byte from a

variable to the device. PUT is used the same as GET. For example:

PUT #1,OUT

In assembly language, the command byte of the IOCB is loaded with the

put-character code (PUTCHR = $0B). Otherwise the PUT command is

identical to GET.

CLOSING A CHANNEL

Closing a channel frees it for use by another device or for changing

parameters. In assembly language the close code is put into the

command byte of the IOCB then the CIOV call is made.

IOCB close command:

CLOSE = $0C

LDX IOCB1

LDA CLOSE

STA ICCOM,X

JSR CIOV

In BASIC, use the CLOSE command followed by the channel number.

CLOSE #1

With the disk drive, the file name is not put into the directory until

the channel is closed.

THE DEVICE TABLE

CIO uses a jump table located at $031A (794). When a CIO call is

made, CIO searches the table for the one-byte device name. The two

bytes following the device name contain the address of the device

handler's vector table. CIO searches the device table from the end,

$033D (829) to the beginning. This way, if a custom handler has ben

substituted for a resident handler, the custom handler will be found

first. (custom handlers cannot be inserted directly in the place of

resident handlers in the device table.)

Each handler has its' own vector table. This vector table is 16 bytes

long. The two-byte vectors point to the various handler routines.

The vectors are stored in the vector table in the following order:

Handler vector table order

open

get byte

put byte

get stat

special

JMP init code (3 bytes)

The open routine should validate the ICAX parameters and check for

illegal commands.

The close routine should send any remaining data in the buffer to the

device, mark the End-Of-File and update any directories, etc.

The get byte routine should get a byte from the device or the handler

buffer and put it in the 6502 A register. Handlers with long timouts

must monitor the break key flag and put a $80 in the 6502 Y register

if the [BREAK] key is pressed.

The put byte routine should send the byte in the 6502 A register to

the device or handler buffer. If the buffer fills, it should be sent

to the device. BASIC can call the put byte routine without using

CIO.

The get status routine may get 4 bytes of status information from the

device and put them in DVSTAT [$02EA] to DVSTAT+3.

For special commands the handler must examine the command byte and

find the proper routine entry point.

In all cases the status (error code) of the operation should be put in

the 6502 Y register.

To be compatible with all versions of the operating system, the

handler must redirect DOSINI [$000C,2 (12)] for initialization upon

reset. This initialization must restore the vectors in the handler

vector table and jump to the origional DOSINI vector.

SPECIAL COMMANDS

Some devices have special CIO commands. These are known as device

specific commands. In assembly language these commands are executed

just as any other CIO command is. In BASIC the XIO command is used.

An example of the XIO command is:

XIO command code #channel,aux1,aux2,device:file name

To open a channel with the XIO command instead of the OPEN command

use:

XIO 3 #1,4,0,"K:"

Note that the above command is identical to the OPEN command except

"XIO 3" is used instead of "OPEN". Also note that $03 is the IOCB

open code for ICCOM.

Useful database variables and OS equates

DOSINI $000C,2 (12): initialization vector

BRKKEY $0011 (17): break key flag

ICHID $0340 (832): start of IOCBs

ICDNO $0341 (833):

ICCOM $0342 (834):

ICSTA $0343 (835):

ICBAL $0344 (836):

ICBAH $0345 (837):

ICPTL $0346 (838):

ICPTH $0347 (839):

ICBLL $0348 (840):

ICBLH $0349 (841):

ICAX1 $034A (842):

ICAX2 $034B (843):

HATABS $031A,16 (794): device handler table

CIOV $E456 (58454): CIO entry vector

THE DISK OPERATING SYSTEM (D:)

The disk operating system program (DOS) is also called the file

management system (FMS). DOS is not a permanent part of the computer,

it is loaded in upon power-up if a disk drive is attached to the

computer.

When the computer is turned on, one of the first things it does is

send a request to the disk drive to load DOS into the computer. This

startup operation is called booting. The word boot is short for

bootstrapping -- the start-up process of early computers. The term

comes from "lifting one's self by one's boot straps".

Anytime the disk boots, the computer tries to read a program starting

at sector 1 and continuing in sequence. If the disk has DOS on it,

the first three sectors, called the boot record, have a program which

loads the DOS.SYS file. If there is no DOS.SYS file on the disk the

computer will display:

--------------------

| BOOT ERROR |

| (etc.) |

| |

--------------------

When a disk is formatted, the drive read/write head passes over the

entire disk and puts magnetic marks on it. These marks divide the

disk into 32 concentric tracks. With DOS 2.0 each track is divided

into 18 sectors, each holding 128 bytes of data. With DOS 2.5 there

are 32 sectors per track giving a total of 1,024 sectors.

Each sector on the disk is marked with a reference number from 1 to

720. Unfortunately, the writers of DOS 2.0 didn't know this so they

wrote the DOS to use sectors numbered from 0 to 719. As a result, DOS

2.0 cannot access sector 720. The designers of the disk drive were

the guilty party in this case. It is normal to number from 0 in

computers. With DOS 2.5, sectors 720 - 1,024 can be accessed

normally.

Sector 720 can be accessed using the computer's resident disk handler.

Some software writers use sector 720 to hide special information to

make their programs difficult to copy.

DOS 2 SECTOR ASSIGNMENTS

Sectors 1 through 3 are called the boot record. They contain a

program which loads the DOS.SYS file into memory.

Sector 360 is called the Volume Table of Contents or VTOC. The main

purpose of the VTOC is to keep track of what sectors are occupied.

Bytes 3 and 4 of the VTOC tell how many sectors are available.

Starting at byte 10 is the Volume Bit Map. Each byte in the VBM tells

the status of eight sectors. If a bit is a 1 the sector is available.

If a bit is a 0 the sector is occupied.

Sectors 361 through 368 contain the disk directory. Each directory

sector holds eight file names. The first byte of a file name is

called the flag byte. It tells the status of that file.

Directory flag byte.

7 6 5 4 3 2 1 0

-----------------

| flag byte |

-----------------

Bits: 7 1 = file deleted

6 1 = file in use

5 1 = file locked

0 1 = open for output

The next two bytes tell how many sectors are in the file. The two

bytes after them tell the starting sector of the file. The last 11

bytes contain the file name.

Sector 720 cannot be accessed with DOS 2.0.

The boot record, VTOC, directory and sector 720 use 13 sectors. This

leaves 707 sectors for storing files with DOS 2.0.

Each file sector has 125 bytes of data. The last three bytes tell how

many bytes of the sector are used, what directory entry the sector

belongs to and which sector is next in the file.

File sector structure

7 6 5 4 3 2 1 0

-----------------

| data | byte 0

- - - -

| bytes | byte 124

-----------------

| Dir. No. |hi | byte 125

-----------------

|forward pointer| byte 126

-----------------

|S| byte count | byte 127

-----------------

hi = high 2 bits of forward pointer

S = Short sector flag. 1 = short sector (End Of File)

If the directory number does not match the order of the file name in

the directory, an error 167 (file number mismatch) will occur.

As a file is written to an empty disk it is put in consecutive

sectors, 125 bytes at a time. After the file is written, the VTOC and

directory are updated. When new files are written they also use

consecutive sectors.

When a file is deleted the status bit of the directory is changed to

show that the file has been deleted. DOS then tracks the file, sector

by sector, to find what sectors are used. Finally the VTOC is updated

to show that the deleted file's sectors are available for new files.

The file is not erased from the disk; only the VTOC and directory are

changed.

When a file is deleted, an "island" of free sectors may be left on the

disk. When a new file is then written to the disk it will first use

these new free sectors. When the island is used up, DOS will skip

over the occupied sectors to the next free sector. This is the reason

for the sector link. A file can end up with it's sectors scattered

all over a disk. It can be complicated but it's efficient.

DISK FILE STRUCTURE

The first few bytes of a file may tell DOS or another program what

kind of file it is. These information bytes are called a header.

A text file is any file which has no header. A listed BASIC program

is a type of text file. A letter from a word processor is another.

A binary load file is a file intended to load to a specific address in

memory. The first two bytes of a binary load file are decimal 255.

The next two bytes hold the address at which the file is to load. The

last two header bytes tell the ending address for the file. If the

file is a program and is to run automatically, the initialization and

run address are appended to the end of the file.

binary load file header

Decimal Hexadecimal

255 identifier FF

255 FF

0 start 00

7 07

15 end FF

8 08

The above file would load at address $0700 (1792 decimal) and end at

address $08FF (2063). If a binary load file has initialization and

run address appended to it they take on the following format:

Init and run tailer

CHR Decimal Hexadecimal

init address format

[b] 226 identifier E2

| 2 02

[c] 227 E3

| 2 02

n address nn

n nn

run address format

[diamond] 224 identifier E0

| 2 02

[a] 225 E1

| 2 02

n address nn

n nn

[ ]=inverse video

A program which doesn't need special initialization can be run at the

init address. Otherwise, an RTS instruction is expected at the end of

the initialization section. The computer will then jump to the run

address if specified.

INSIDE THE COMPUTER

DOS uses the computer's CIO utility. When a DOS disk is booted a

non-resident handler is loaded into memory. A new handler name, D, is

then added to the handler table. When CIO is called with a device

name of D: or Dn:, CIO will search the handler table for that device

name. If the 'D' is found, the next two bytes in the table point to

the DOS entry address.

DOS FILE NAME CONVENTIONS

DOS is unique among CIO handlers in that it requires an eight

character file name to follow the device name. This file name may be

followed by a period and then a three character extender.

EXAMPLES: D:TEST, D2:FIREMAN, D:VENTURE.EXE, D:CHAPTER.001

The D2: is used for drive number two if present.

The file name must use upper-case letters or numbers. The first

character must always be a letter.

WILD CARDS

The characters * and ? may be used as wild cards. * means any

combination of characters and ? means any single character.

EXAMPLES: D:P* any file beginning with P and

without an extender

D:*.EXE any file with the extender .EXE

D:*.* any file.

D:F?REMAN one unknown character,

FIREMAN or FOREMAN will match

Wild cards can only be used to load, delete, lock and unlock files.

When loading a file using wild cards, only the first matching file

will be loaded.

When renaming a file, both the new and old names are expected after

the device name.

EXAMPLE: D:OLDNAME.BAS,NEWNAME.BAS

To format a disk, only the device name (D: or Dn:) is needed.

USING DOS

When a CIO channel is opened to the disk drive it must actually be

opened to a specific file on the disk. The device name in the open

command must be followed by a file name.

When a channel is opened to the disk, two special parameters may be

used in ICAX1.

ICAX1 for disk open:

7 6 5 4 3 2 1 0

-----------------

| W R D A|

-----------------

D 1 = open to read the directory instead of a file

A 1 = append data to the end of the file

This gives the following extra ICAX1 options.

Disk specific ICAX1 options:

HEX DEC

$06 6 open to read directory

$09 9 output, append to the end of an

existing file

READING THE DIRECTORY

When the directory is read, each file name is treated as if it were

followed by an EOL. A loop must be used to read all of the file names

in the directory. The last entry read is the free sector count.

After it is read, another read operation will result in an End-Of-File

error.

The disk drive has a number of device specific commands other than the

regular CIO commands. From BASIC the XIO command is used to access

these commands. The XIO command allows you to directly load the IOCBs

from BASIC. Each parameter of the XIO command places values in

certain bytes of an IOCB.

XIO command format:

XIO command channel,aux1,aux2,device:file name

Note that the parameters resemble the BASIC OPEN command. The BASIC

OPEN command is identical to it's equivalent XIO command.

XIO commands specific to the disk drive.

RENAME XIO $20 (32)

DELETE XIO $21 (33)

LOCK XIO $23 (35)

UNLOCK XIO $24 (36)

POINT XIO $25 (37)

NOTE XIO $26 (38)

FORMAT XIO $FE (254)

EXAMPLES:

XIO 33 #1,0,0,"D:JUNK" = delete file named D:JUNK

XIO 32 #1,0,0,"D:OLD,NEW" = change name of D:OLD to D:NEW

NOTE and POINT can also be used directly from BASIC. NOTE finds the

current position of the read/write head on the disk. POINT moves the

read/write head to the desired position.

USING NOTE AND POINT

The command format for NOTE and POINT is as follows:

NOTE \

channel,sector,byte

POINT/

EXAMPLE:

NOTE #1,SECT,BYTE

BASIC requires the sector and byte parameters in both commands to be

variables. Fixed numbers cannot be used. If you try to do a POINT to

a sector outside the file the channel is open to, a point error will

occur. Care may need to be taken to be sure the file being accessed

is in contiguous sectors on the disk. If it is not, it will be

difficult to know where to do points to.

One use of NOTE is to use the command immediately after opening a

channel to a disk file. After the NOTE command, the parameter

variables contain the coordinates of the first byte of the file. They

can then be used as a reference for the POINT command.

In assembly language, ICAX3 and ICAX4 are used for the sector number

(lsb,msb). ICAX5 is used for the byte number.

STATUS REQUEST

If the status request command is used, one of the following values

will be found in ICSTA and the 6502 Y register.

HEX DEC

$01 1 OK

$A7 167 file locked

$AA 170 file not found

USING THE DOS 2 UTILITIES (DUP.SYS)

If you boot a DOS disk with no cartridge in the slot or with BASIC

disabled (by holding the OPTION key), DOS will try to load the file

named DUP.SYS. This is the disk utility file. When using BASIC,

typing DOS [RETURN] will load the DUP.SYS file. When the utilities

are loaded the menu will appear on the screen.

THE DOS UTILITIES MENU

DISK OPERATING SYSTEM II VERSION 2.0S

A. DISK DIRECTORY I. FORMAT DISK

B. RUN CARTRIDGE J. DUPLICATE DISK

C. COPY FILE K. BINARY SAVE

D. DELETE FILE(S) L. BINARY LOAD

E. RENAME FILE M. RUN AT ADDRESS

F. LOCK FILE N. CREATE MEM.SAV

G. UNLOCK FILE O. DUPLICATE DISK

H. WRITE DOS FILES

SELECT ITEM OR [RETURN] FOR MENU

[A] DIRECTORY

After pressing [A] [RETURN] you will get the prompt:

DIRECTORY--SEARCH SPEC,LIST FILE?

If you want to see the entire directory just press [RETURN] again. If

you wish, you may type in a specific file name (D: is optional) or

wild cards to search for. If you specify a search spec only matching

files will be displayed.

If you want, you can have the directory sent to another device. To do

this type a comma and the device name. For example, if you type ,P:

the directory will be sent to the printer.

[B] RUN CARTRIDGE

If a cartridge was inserted or BASIC was not disabled when the

computer was turned on, [B] [RETURN] will run that cartridge or

BASIC.

[C] COPY FILE

This option will copy a file to another part of the same disk (with a

different file name) or copy from one disk drive to another. When you

press [C] [RETURN] you will be given the prompt:

COPY--FROM,TO

Type the devices and file names separated by a comma.

EXAMPLES:

FOREMAN,FIREMAN

D1:TEST,D2:TEST

The first example will copy to the same disk. The second example will

copy from disk drive one to disk drive two.

If you want to have the first file appended to the end of the second

file type /A after the file names.

EXAMPLE:

RUNMENU.EXE,AUTORUN.SYS/A

If the files are binary load files, this will cause both files to be

saved as one file. When the load command is used they will both be

loaded and run.

[D] DELETE FILE(S)

After pressing [D] [RETURN] you will get the prompt:

DELETE FILE SPEC

After typing the file name you will be asked to confirm the file to

delete.

DELETE FILE SPEC

DELETE-D1:JUNK ARE YOU SURE?

Press [Y] if the correct file is displayed. If you use wild cards you

will be asked to confirm each matching file.

[E] RENAME

Upon typing [E] [RETURN] you will be given the prompt:

RENAME-GIVE OLD NAME,NEW

Type the file name you want to change and the new name separated by a

comma.

EXAMPLE:

COLT,HORSE

WARNING! Do not rename a file to a name which already exists on the

disk. You will end up with a duplicate file name and will not be able

to access one of them. Attempting to rename or delete one of them

will rename or delete both. The only way to fix a duplicate file name

is with a sector editor or other special utility.

[F] LOCK FILE

A locked file cannot be written to, renamed or deleted. To lock a

file type [F] [RETURN]. You will get the prompt:

WHAT FILE TO LOCK?

Type the file name you want to lock. Wild cards will cause all

matching files to be locked.

[G] UNLOCK FILE

Used the same as lock.

[H] WRITE DOS FILES

This option will write the DOS.SYS and DUP.SYS files to a formatted

disk. When you type [H] [RETURN] you will receive the prompt:

DRIVE TO WRITE DOS FILES TO?

Type the number of the drive. If the drive contains a formatted disk

the dos files will be written to it.

[I] FORMAT DISK

This option formats a new disk or erases a disk with files on it.

Typing [I] [RETURN] will get you the prompt:

WHICH DRIVE TO FORMAT

Be sure you have the correct disk in the proper drive then type the

drive number. It is impossible to recover files on a disk formatted

by accident.

While the disk is being formatted the drive will check to be sure the

disk is formatted correctly. If not, the drive attempt to format the

disk again. If the disk is defective the drive will not finish the

formatting process.

[J] DUPLICATE DISK

This option will copy an entire disk except for sectors listed as free

in the VTOC. Some programs are copy-proofed by changing the VTOC to

show that some occupied sectors are empty. For such disks, a program

which copies the entire disk is needed.

When you press [J] [RETURN] you will be given the prompt:

DUP DISK--SOURCE,DEST DRIVES?

If you are using only one disk drive, type 1,1. If you have only one

drive you will be told when to swap disks.

[K] BINARY SAVE

This option saves a block of memory as a binary load file. When you

type [K] [RETURN] you will be given the prompt:

SAVE-GIVE FILE,START,END(,INIT,RUN)

Type the desired file name and a comma. Now type the start and end

addresses of the memory block to be saved, in hexadecimal numbers,

separated by commas. If the file is a program which is to

automatically run when loaded, give the initialization address, if

needed, then the run address.

EXAMPLE:

CHASE.EXE,0700,09FF,,0700

This will save the block of memory from address 0700 to 09FF. The

program is not initialized before running so there is no address typed

after the third comma. When the program is loaded the computer will

jump to address 0700, as specified in the last parameter, to run the

program.

[L] BINARY LOAD

To load a binary file type [L] [RETURN]. You will get the Prompt:

LOAD FROM WHAT FILE?

Type the file name and the file will be loaded. If wild cards are

used, only the first matching file will be loaded.

[M] RUN AT ADDRESS

Typing [M] [RETURN] will get the prompt:

RUN FROM WHAT ADDRESS?

Type the hexadecimal address of the program you want to run.

[N] CREATE MEM.SAV

A MEM.SAV file is used by BASIC and some other programs to save the

part of memory which the DUP.SYS file loads into. If there is no

MEM.SAV file on the disk when you go to the DOS utilities, you will

loose that part of memory. With BASIC you will loose your program.

When you type [N] [RETURN] you will get the prompt:

TYPE Y TO CREATE MEM.SAV

Typing [Y] [RETURN] will create a MEM.SAV file on the disk in drive

one.

[O] DUPLICATE FILE

This option is used to copy a file from one disk to another, using

only one disk drive. When you type [O] [RETURN] you will get the

prompt:

NAME OF FILE TO MOVE?

If you use wild cards you will be asked to swap disks for each

matching file.

DOS 2.5 also has option:

[P] FORMAT SINGLE

DOS 2.5 normally formats disks to use "enhanced" density. This option

will format a disk in single density for use with the 810 drive.

DOS 2.5 also has some special utilities on the master disk. Use the

binary load option to run them.

RAMDISK.SYS

This program will cause the extra bank of memory in the 130XE to act

like a disk drive (called D8:). If this program is on the disk it

will automatically run. It need not be renamed to AUTORUN.SYS.

COPY32.COM

Copies DOS 3 files to DOS 2.

DISKFIX.COM

Can make certain "repairs" to a disk, such as restoring deleted

files.

SETUP.COM

Used to change the default configuration of DOS.

AUTORUN.SYS (DOS 2.0 and 2.5)

This program is needed to operate the RS-232 ports on the 850

interface. If you don't want this program to automatically load when

you boot with the master disk, rename the file to RS232.

SPECIAL DOS INFORMATION

When DOS is in memory, changes can be made to the DOS program. These

changes can be made by poking the changes into memory. If you want to

make the changes permanent, you can type DOS [RETURN] to load the

utilities. From the utilities menu you can use the write DOS files

option to save the changes on disk. Some of the useful changes you

can make follow.

POKE 1913,80

This turns off the write verify and speeds up disk writing.

POKE 1913,87

This turns write verify on

POKE 5903,42

POKE 5904,46

POKE 5905,82

POKE 5906,85

POKE 5907,78

POKE 5908,155

This causes any binary file with the extender .RUN to be loaded

automatically when the computer is turned on.

POKE 5903,65

POKE 5904,85

POKE 5905,84

POKE 5906,79

POKE 5907,82

POKE 5908,85

This returns the DOS to normal, Automatically loading files named

AUTORUN.SYS.

DOS 2.0 DOS 2.5

POKE 3772,255

POKE 3818,64 POKE 3774,64

POKE 3822,123 POKE 3778,123

This will cause DOS to accept lower-case as well as upper-case letters

in file names. It will also now accept @,[,\,],^ and _ .

POKE 3772,223

POKE 3818,65 POKE 3774,65

POKE 3822,91 POKE 3778,91

This will change DOS back to normal, accepting only upper-case letters

and numbers.

THE CASSETTE HANDLER (C:)

The cassette handler sends data to the cassette recorder in blocks of

128 bytes each. The blocks are sent in the following format:

Cassette record format

-----------------

|0 1 0 1 0 1 0 1| speed measurement bytes

-----------------

|0 1 0 1 0 1 0 1|

-----------------

| control byte |

-----------------

| 128 |

= data =

| bytes |

-----------------

| checksum | handled by SIO

-----------------

The control byte may have one of the following values.

$FC (252) record is full.

$FA (250) partly full, next record is EOF.

$FE (254) EOF record, data section is all zeroes.

The cassette handler has two modes of operation. The first mode uses

only a short gap between records. It is called the no IRG

(interrecord gaps) mode. The second mode uses longer gaps between

records and is called the IRG mode. In the IRG mode the computer may

stop the cassette recorder between records for processing data.

When a channel is opened to the cassette recorder, bit 7 of ICAUX2 may

be set to 1 (ICAX2 = $80 (128)). This will cause the cassette to use

the no IRG mode.

A cassette file starts with a 20 second mark tone. This tone is

followed by the file records with 128 data bytes each. The final

record is an End-Of-File record.

The cassette is a straight-forward read/write device. There are no

special functions other than those common to other CIO devices.

The cassette motor is controlled by one of the controller port control

registers. If bit 3 of PACTL [$D302 (54018)] is 0 then the cassette

motor is on. The following BASIC commands will turn the cassette

motor on and off.

Cassette motor control.

POKE 54018,PEEK(54018)-8 motor on

POKE 54018,PEEK(54018)+8 motor off

Useful data base variables and OS equates

PACTL $D302 (54018): port A control register, bit 4

controls cassette motor

THE KEYBOARD HANDLER (K:)

The keyboard is a read only device and therefore the keyboard handler

has no output functions.

The keyboard handler reads the keys as ATASCII codes. Each key is

represented by one byte of data. Therefore, each time a key is

pressed the data is treated as a byte of data just as data from any

other device is. The only difference is that the computer must wait

for the operator to press the keys as it reads the data.

Whenever a key is pressed an IRQ interrupt is generated by the

keyboard reading hardware. The internal code (not ATASCII) for the

key just pressed is then stored in CH [$02FC (764)]. The code is then

compared with the prior key code in CH1 [$02F2 (754)]. If the code in

CH1 is different from the code in CH, the key is accepted. The code

is then converted to ATASCII, and placed in the database variable

ATACHR [$02FB (763)]. On XL and XE models, KEYDEF [$0079,2 (121)]

points to the key-code-to-ATASCII conversion table. (This address is

used by the the screen handler in 400/800 models).

If the code in CH1 is the same as the code in CH, the new key code

will not be accepted unless the key debounce timer, KEYDEL [$02F1

(753)] is 0.

When CIO is told to do an input operation from the keyboard, CH is

checked to see if a key has been pressed. If CIO finds $FF (255) in

CH, it waits until a key is pressed. If CH is not $FF, a key has been

pressed and the ATASCII code for that key is taken from ATACHR. CH is

then set to $FF.

The data in CH is in the following format.

Key code format:

7 6 5 4 3 2 1 0

-----------------

|C|S| key code |

-----------------

C 1 = [CTRL] key is pressed

S 1 = [SHIFT] key is pressed

Anytime a key is pressed, CH is loaded with the key code. CH will

hold the code until the computer is commanded to read the keyboard.

Sometimes the computer will read a key which was pressed long ago. If

you want to prevent this, load CH with $FF before reading the

keyboard. (In BASIC use POKE 764,255.) This will clear out any old

key pressings.

Special function keys

[CTRL][1] screen output start/stop

[CTRL][2] BELL

[CTRL][3] Generates End-Of-File status

[/|\]

[/] inverse video toggle

[CAPS LOWER] sets lower case

[CTRL][CAPS] sets CTRL lock

[SHIFT][CAPS] sets caps lock

KEYBOARD REPEAT DELAY AND RATE CONTROL

On the XL and XE, KRPDEL [$02D9 (729)] determines the delay before the

key repeat begins. The value of this byte is the number of vertical

blanks (1/60th second each) to delay. KEYREP [$02DA (730)] determines

the repeat rate in vertical blanks.

KEYBOARD CLICK

The keyboard click of the XL/XE is heard through the TV speaker. The

click may be turned off by putting $FF in NOCLIK [$02DB (731)].

NON-HANDLER, NON-CIO KEYS

The [OPTION], [SELECT] and [START] keys are read from the console

switch register, CONSOL [$D01F (53279)].

The console switch register

7 6 5 4 3 2 1 0

-------------------------

CONSOL |0 |0 |0 |0 |SP|OP|SE|ST|

-------------------------

8 4 2 1

ST 0 = [START]

SE 0 = [SELECT]

OP 0 = [OPTION]

SP Console speaker. set to 1 during vertical blank.

toggleing this bit operates the speaker (which

is heard through the TV on XL/XE models).

This bit always reads 0

The [HELP] key on XL and XE models is read from HELPFG, [$02DC (732)].

This address is latched and must be reset to zero after being read.

The [HELP] key register

7 6 5 4 3 2 1 0

-----------------

HELPFG |C S 0 H 0 0 0 H|

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

H 1 = [HELP] (bits 0 and 4)

S 1 = [SHIFT]

C 1 = [CONTROL]

Useful database variables and OS equates

KEYDEF $0079,2 (121): key code coversion table vector (XL/XE)

KRPDEL $02D9 (729): delay before key repeat (XL/XE)

KEYREP $02DA (730): key repeat rate (XL/XE)

NOCLIK $02DB (731): $FF turns off key click (XL/XE)

HELPFG $02DC (732): [HELP] key (XL/XE)

ATACHR $02FB (763): ATASCII Code for last key

CH $02FC (764): keycode, $FF if no key has been pressed

BRKKEY $0011 (17): break key flag, 0 = break key pressed

SRTIMR $022B (555): Key delay and repeat timer

SHFLOK $02BE (702): SHIFT/CTRL lock flag

$00 = lower case

$40 (64) = upper case lock

$80 (128) = CTRL lock

INVFLG $02B6 (694): inverse video flag, non-zero = inverse

CONSOL $D01F (53279): start, select and option keys

IRQEN $D20E (53774): IRQ interrupt enable

bit 7 enables [BREAK]

bit 6 enables other keys

shadow registers

POKMSK $0010 (16): IRQEN shadow

THE PRINTER HANDLER (P:)

The printer is a write only device so the printer handler has no input

functions. The printer handler has no special functions other than

the CIO functions common to all other devices.

Although many printers have special functions, the printer handler has

no control over them. See your printer manual for information on

special functions.

SCREEN EDITOR (E:)

The screen editor uses both the keyboard handler and the screen

handler to provide interactive control of the computer. In fact, the

keyboard handler, the screen handler and the screen editor are

contained in a single section of code and are therefore very closely

related.

The editor works with one line of characters at a time. The lines it

works with are called logical lines and are up to three screen lines

long.

The screen editor inputs data from the keyboard and then prints the

data on the screen. When the [RETURN] key is pressed, the editor

inputs all of the data on the present logical line for processing by

CIO.

If characters are typed on the screen, and then the cursor is moved

off the line, then back on the line, and new characters are typed,

only the characters to the right of the reentry point of the cursor

are input when [RETURN] is pressed. However, if the cursor is moved

off the line again, then moved back on, all characters on that logical

line are input.

If bit 0 of ICAX1 is 1, the editor will act as if the [RETURN] key is

being held down. This bit may be changed at any time.

Editor control codes

The screen editor treats certain ATASCII codes as special control

codes.

Screen editor control codes

KEY HEX DEC FUNCTION

[RETURN] $9B 155 carriage return or EOL

[CLEAR] $7D 125 Clear screen,put cursor in upper left

[UP ARROW] $1C 28 Move cursor up one screen line

[DOWN] $1D 29 down one line

[LEFT] $1E 30 left one character

[RIGHT] $1F 31 right one character

[BACK S] $7E 126 Back-space operation

[SET TAB] $9F 159 sets tab stop at cursor

[CLEAR

TAB] $9E 158 Clear tab stop at cursor

[TAB] $7F 127 move to next tab stop

[SHIFT]

[INSERT] $9D 157 Make space for a new line

[SHIFT]

[DELETE] $9C 156 delete the logical line at the cursor

[CTRL]

[INSERT] $FF 255 make room for a character

[CTRL]

[DELETE] $FE 254 delete character at cursor

[ESCAPE] $1B 27 causes next non-EOL code to be

displayed as an ATASCII character, even if it is an editor

control code

[CTRL][1] screen print start/stop

[CTRL] $FD

THE DISPLAY HANDLER (S:)

The display handler manages the computer's video display. Although no

data ever leaves the computer through it, the display is treated like

any other CIO device. Data sent to the screen may be displayed as

either characters or point by point graphics. Although it is only

visible in the 40 column text mode, mode 0, there is a cursor on the

screen in all of the text or graphics modes. Whenever a character or

graphics point is put on the screen, the cursor moves just as in mode

The display is capable of both input and output. Information can be

put on the screen with any of the CIO output commands. An input

command will find whatever is on the screen at the position of the

cursor.

When text or graphics is sent to the screen it is actually stored in

an area of memory called the display buffer. What you see on the

screen is the computer's interpretation of the data stored there.

This will be explained further as each mode is covered.

DISPLAY HANDLER SPECIAL FUNCTIONS:

DRAW

FILL

SPECIAL ERROR STATUSES:

$84 (132) Invalid special command.

$8D (141) Cursor out of range.

$91 (145) Nonexistant screen mode.

$93 (147) Insufficient ram for screen mode.

TEXT MODE 0

In graphics mode 0, data passes through CIO, and is stored in the

display buffer in the following format.

7 6 5 4 3 2 1 0

-----------------

|I| Data |

-----------------

I 1 = displays character in inverse video.

Bits 0 through 6 select one of the 128 characters in the ATASCII set.

If bit seven = 1, the character is displayed in inverse video.

Converting the above byte to decimal will give the BASIC ASC(x)

equivalent.

The characters displayed in the text modes are determined by tHE

ATASCII character set. This is a bit by bit representation of how the

characters appear on the screen. The character set starts $E000

(57344) in the operating system ROM. From there, for 1K of memory,

each eight bytes holds a "bit map" of a particular character. Below

is how the letter A is stored in the character set.

Letter A as represented in the C-set

7 6 5 4 3 2 1 0

-----------------

$E208 |0 0 0 0 0 0 0 0|

-----------------

|0 0 0 1 1 0 0 0| * *

-----------------

|0 0 1 1 1 1 0 0| * * * *

-----------------

|0 1 1 0 0 1 1 0| * * * *

-----------------

|0 1 1 0 0 1 1 0| * * * *

-----------------

|0 1 1 1 1 1 1 0| * * * * * *

-----------------

|0 1 1 0 0 1 1 0| * * * *

-----------------

$E20F |0 0 0 0 0 0 0 0|

-----------------

XL and XE models have an international character set starting at $CC00

(55224). In this character set the graphics characters are replaced

by international characters.

Custom characters sets may be loaded at any free address which is a

multiple of 1,024 ($0400, or 1K). The database variable CHBAS [$02F4

(756)] stores the most significant byte (MSB) of the address of the

active C-set. Since the LSB of the C-set address is always $00, no

LSB is needed to find it.

The data stored in the display buffer does not use the ATASCII code.

A special code needed by the ANTIC chip is used.

DISPLAY CODE / ATASCII CODE CONVERSION:

ATASCII display

$00 - $1F ( 0 - 31) = $40 - $5F (64 - 95)

$20 - $5F (32 - 95) = $00 - $3F ( 0 - 63)

$60 - $7F (96 - 127) = unchanged

The codes for inverse video (the above codes with bit 7 set (= 1) or

the above codes + 128 in decimal) are treated likewise.

When you first turn on the computer, BASIC opens channel 0 to the

screen editor (E:). The screen editor uses both the keyboard handler

and the screen handler, in mode 0, to display characters when they are

typed in.

TEXT MODES 1 AND 2

Graphics modes 1 and 2 offer a split screen configuration if desired.

The split screen has four lines of mode 0 at the bottom of the

screen.

In mode 1 the screen holds 20 characters horizontally and 24

characters vertically. In mode 2 the characters are twice as tall so

the screen holds 12 vertically.

In BASIC, characters are sent to the screen with the PRINT command.

Since BASIC uses channel 6 for graphics you must specify channel 6 in

the command. For example:

? #6;"HELLO"

If you use a comma in place of the semicolon, ten spaces will print

before the "HELLO"

You can also use the PLOT and DRAWTO commands. In this case the COLOR

command determines the character, as well as the color to be

displayed.

Data passes through CIO in the following form:

7 6 5 4 3 2 1 0

-----------------

| C | D |

-----------------

C determines the color.

C Default Color Shadow

Color Register Register

0 green COLPF1 COLOR1

1 gold COLPF0 COLOR0

2 gold COLPF0 COLOR0

3 green COLPF1 COLOR1

4 red COLPF3 COLOR3

5 blue COLPF2 COLOR2

6 blue COLPF2 COLOR2

7 red COLPF3 COLOR3

D is a 5 bit ATASCII code which selects the character to be displayed.

The database variable CHBAS selects between upper case (CHBAS=$E0

(224)) and lower case (CHBAS=$E2 (226)).

GRAPHICS MODES 3 THROUGH 11

Modes 3 through 8 offer a split screen mode. In modes 9 through 11

special programming is required for split screens.

These modes use dot by dot (pixel by pixel) graphics instead of

character sets. Before explaining how graphics are sent to the screen

through CIO, I will describe how the data in the display buffer is

interpreted by the ANTIC chip.

Mode 8 is the simplest of the graphics modes. Each byte of the

display buffer controls eight pixels horizontally. The first 40 bytes

of the display buffer control the first horizontal line of graphics.

This makes a total of 320 pixels horizontally. If one of the eight

bits of a byte is a 1 then the pixel it controls is on. If a bit is a

0 then it's pixel is off. For example, if a particular byte is equal

to $9B (binary 10011011) then its' part of the screen would look

like...

* ** **

(10011011)

In reality the pixels are assigned to different color registers. A

color register is a byte of memory which controls the color of all

pixels assigned to it. In mode 8, if a bit is = 0 it's pixel is

assigned to the register called COLBK. If a bit is one, it's pixel is

assigned to COLPF0. See COLORS below for more information on the

color registers.

You may notice a close similarity between mode 0 and mode 8. The

major difference between these modes is where the dot by dot

information comes from. In mode 8 this information comes from the

display buffer. In mode 0 the display buffer contains codes telling

what characters to display. The actual dot by dot information comes

for the character set at $E000.

In mode 7 each pixel is controlled by two bits. Therefore each byte

only controls four pixels. There are also only 1/4 as many pixels on

the screen as in mode 8. See mode 3 below for an explanation of how

the each byte affects the pixels.

In a graphics mode, when CIO sends a byte of data to the screen

handler, that byte has information for only one pixel. Do not confuse

a byte which CIO sends to the screen handler with the bytes in the

display buffer.

CIO sends data to or retrieves data from the screen in the following

forms.

7 6 5 4 3 2 1 0

-----------------

|0 0 0 0 0 0| D | Modes 3,5,7 -- D = color

-----------------

|0 0 0 0 0 0 0|D| Modes 4,6,8 -- D = Color

-----------------

|0 0 0 0| D | Modes 9,10,11 -- D = data

-----------------

Mode 3 uses a screen which is 40 pixels horizontally and 24

vertically. Each pixel is a square the size of a mode 0 character.

It requires 273 bytes of RAM where each byte controls 4 pixels. Each

pair of bits controls which of the four color registers their pixel is

assigned to.

display buffer byte for mode 3

7 6 5 4 3 2 1 0

-----------------

| D | D | D | D |

-----------------

P1 P2 P3 P4

Pixel/color register assignments:

D = 00 COLBK (COLOR4)

01 COLPF0 (COLOR0)

10 COLPF1 (COLOR1)

11 COLPF2 (COLOR2)

Mode 4 uses a screen of 80 columns by 48 rows. Each pixel is half the

size of those in mode 3. Mode 4 requires 537 bytes of RAM where each

byte controls 8 pixels. This mode is very similar to mode 8 except

there are fewer but larger pixels.

Mode 5 uses a screen of 80 columns by 48 rows. The pixels are the

same size as in mode 4. Mode 5 requires 1,017 bytes of RAM where each

byte controls 4 pixels in the same manner as in mode 3.

Mode 6 uses a screen of 160 columns by 96 rows. It requires 2,025

bytes of RAM where each byte controls 8 pixels as in mode 4.

Mode 7 uses a screen of 160 columns by 96 rows. It requires 3,945

bytes of RAM where each byte controls 4 pixels as in modes 3 and 5.

Modes 8 through 11 (and 15 on XL and XE models) each require 7,900

bytes of RAM and are very similar in display set up. The main

differences between these modes is the interpretation of data in the

display buffer.

Mode 15 (sometimes called mode 7.5) uses a screen of 160 columns by

192 rows. Each byte controls 4 pixels as in mode 7. The main

difference between mode 15 and its related modes is bit 0 of each

instruction byte in the display list (the program which the ANTIC chip

uses). If this bit is 0 the screen is interpreted as mode 15. If the

bit is 1 the screen is interpreted as modes 8 through 11.

Modes 8 through 11 are set up identically in memory, including the

display list. The only difference is the data in the PRIOR register

of the GTIA chip. The shadow register for PRIOR is GPRIOR [$026F

(623)].

Mode 8 (PRIOR = $00 - $3F (0 - 63)), uses a screen of 320 columns by

192 rows. Each byte controls 8 pixels as in modes 4 and 6.

Mode 9 (PRIOR = $40 - $7F (64 - 127)) uses a screen of 80 columns by

192 rows. Each byte controls 2 pixels. The pixels are all of the

same color, controlled by COLBK. Each half of a byte in the display

buffer controls the luminance of the assigned pixel. The format of

each byte is as follows.

7 6 5 4 3 2 1 0

-----------------

| data | data |

-----------------

pixel 1|pixel 2

Mode 10 (PRIOR = $80 - $BF (128 - 191), is the same as mode 9 except 9

color luminance combinations are available. The data in each half

byte chooses one of the 9 color registers for the assigned pixel.

Mode 11 (PRIOR = $C0 - FF (192 - 255), is the same as mode 9 except

there is one brightness but 16 colors. The pixel data chooses one of

the 16 available colors. The luminance is that of the background

(COLBK).

USING THE SCREEN HANDLER

OPENING A CHANNEL TO THE SCREEN HANDLER

When a channel is opened to the screen handler the following actions

take place:

The area of memory to be used for the screen data is cleared.

A display list (program for the ANTIC chip) is set up for the proper

graphics mode.

The top-of-free-memory pointer, MEMTOP [$02E5,2 (741)], is set to

point to the last free byte before the display list.

Before opening a channel to the screen handler, the pointer to the

highest memory address needed by the program, APPMHI [$000E,2 (14)],

should be properly set. This will prevent the screen handler from

erasing part of the program when it sets-up the screen data region.

When the channel is opened, two special options can be sent with the

direction parameter (ICAX1).

ICAX1 for screen open

7 6 5 4 3 2 1 0

-----------------

| C S W R |

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

C 1 = don't clear the screen

S 1 = split screen

R 1 = input

W 1 = output

Before the open command, the graphics mode number is placed into

ICAX2.

ICAX2 for screen open

7 6 5 4 3 2 1 0

-----------------

| : mode |

-----------------

mode = $00 through $0B (0 - 11 (0 - 15 on XL/XE))

To open a channel to the screen in BASIC use the GRAPHICS command.

BASIC screen open format

GRAPHICS mode

For Example:

GRAPHICS 8

This will set up a mode 8 graphics screen and open channel 6 to it.

If the graphics mode is 1 - 8, a split screen will be set up. For

example, GRAPHICS 8 will set up a mode 8 screen with a four line text

window at the bottom.

If 16 is added to the mode number, a full screen will be set-up. For

example, GRAPHICS 8+16 or GRAPHICS 24 will set up a mode 8 screen,

with no text window, a full 192 pixels high. If the number 32 is

added to the mode number, the screen will not clear when the channel

opens.

If you want to use a channel other than #6, you will have to use the

open command. It is used in the following format.

screen open without GRAPHICS command

OPEN #channel,direction/special,mode,S:

For example:

OPEN #1,8,7,S:

This will open channel 1 to a mode 7 screen for output only. For use

of special parameters, see ICAX1 above.

USING AN OPEN CHANNEL TO THE SCREEN

Once a channel is opened to the screen it is used like any other input

or output device. In other words, data is placed on the screen by the

PRINT and PUT commands. Data is retrieved from the screen with the

INPUT and GET commands. The part of the screen which the data will be

put in or taken from is determined by the X,Y coordinants in the

database variables COLCRS [$0055,2 (85)] and ROWCRS [$0054 (84)].

What appears on the screen depends on what graphics mode the computer

is in.

Before sending data to the screen in BASIC, a color register must be

assigned to the data. Once a point is plotted on the screen, it's

color will be determined by the color register it was assigned to.

To assign a color to a ploted point, the COLOR command us used as

follows.

COLOR command format

COLOR register

For example,

COLOR 1

After using the above command, all points plotted will be controlled

by color register 1. To change color registers, use the COLOR command

again.

In assembly language, the color is determined by the data sent to the

screen. See the above section on graphics modes for color

information.

In BASIC the PLOT command is used to put data on the screen. The PLOT

command is used as follows.

The BASIC PLOT command

PLOT x,y

x and y are the horizontal and vertical coordinates for the plotted

point.

In modes 3 through 11 a single point will be plotted. In modes 1 and

2 a text character will be printed on the screen by the PLOT command.

The PRINT and PUT commands can also be used in basic. What appears on

the screen depends on the graphics mode.

In modes 1 and 2 the ATASCII characters sent to the screen will be

printed just as in mode 0. See the paragraph on modes 1 and 2 above

for more information. In the other modes what appears depends on how

the ANTIC chip interprets the data bytes sent to the screen. For

example, in mode 8, even numbered characters will be single pixels in

color 1. Odd numbered characters will be in color 0 (background).

There are two special commands for the screen handler, DRAW and FILL

DRAW (ICCOM = $11 (17))

The draw command works exactly like the plot command except a straight

line is drawn from the previous pixel to the new one. In BASIC it is

used in the following format.

the BASIC DRAW command

DRAWTO x,y

FILL (ICCOM = $12 (18))

Fill works like draw except the area to the right of the drawn line

will be filled with the color in FILDAT [$02FD (765)]. The fill

command expects to find a boundary to the right. If no boundary is

found, the entire horizontal screen between the ends of the line is

filled.

To use the fill command in BASIC the XIO command must be used in the

following format.

POSITION x,y

XIO 18 #6,0,0,"E:"

Note that the cursor is first moved by the POSITION command. Below is

an example of how to prepare for and use the fill command.

using the fill command

2nd DRAWTO .____. DRAWTO here

| |

fill to here ! ! PLOT here

This will draw and fill a box on the screen.

THE COLOR REGISTERS

There are nine bytes of memory which control the colors on the screen.

These bytes are called color registers. The color registers have the

following names and relationships.

Color registers and relationships

name address

0 & 8 1 & 2 3 5 7 4 & 6 9 & 11

HEX decimal COLOR numbers

PCOLR0 $02C0 704

PCOLR1 $02C1 705

PCOLR2 $02C2 706

PCOLR3 $02C3 707

COLOR0 $02C4 708 0 - 63 1 1

COLOR1 $02C5 709 1 - 255 64 -127 2

COLOR2 $02C6 710 0 128-191 3

COLOR3 $02C7 711 192-255

COLOR4 $02C8 712 border backgnd 0 backgnd backgnd

The color numbers are in decimal. These are actually shadow

registers. See the O.S. equates below for relationships. In modes 0

- 3 the COLOR number actually determines the character printed

The register to which a pixel/character is assigned to is determined

by the data byte sent to the screen through CIO.

The data in the color registers in in the following format.

Color register data format

7 6 5 4 3 2 1 0

-----------------

| color |bright |

-----------------

color = one of 16 possible colors

bright = one of 8 possible brightnesses

(even numbers, 0 - E)

In basic, the COLOR command is used to assign color registers. The

corresponding registers depends on the graphics mode. For example,

COLOR 0 is COLOR2 in mode 8. In most other modes COLOR 0 is COLOR4.

See the above chart for the register relationships.

To change the contents of the color registers in BASIC, the SETCOLOR

command is used. In all modes except mode 10, the SETCOLOR command

refers to the registers COLOR0 to COLOR4.

SETCOLOR/register relationships

SETCOLOR 0 COLPF0 (COLOR0)

SETCOLOR 1 COLPF1 (COLOR1)

SETCOLOR 2 COLPF2 (COLOR2)

SETCOLOR 3 COLPF3 (COLOR3)

SETCOLOR 4 COLBK (COLOR4)

The format for the SETCOLOR command is...

SETCOLOR command format

SETCOLOR register,hue,brightness

hue = 0 - 15 (16 colors)

brightness = 0 - 16 (even numbers only (8 brightnesses)

The following chart gives the colors represented by the hue number.

colors represented by hue numbers

0 grey 8 blue

1 gold 9 cyan

2 gold-orange 10 blue-green

3 red-orange 11 blue-green

4 orange 12 green

5 magenta 13 yellow-green

6 purple-blue 14 yellow

7 blue 15 yellow-red

The attract mode

If a key is not pressed for more than 9 minutes the computer will

enter the attract mode. This mode is used to prevent burning of the

TV phosphors by lowering the brightness and constantly changing the

colors. The attract mode timer, ATRACT [$004D (77)], is set to 254

($FE) when the the attract mode is entered. To force the computer out

of the attract mode, poke a number less than 127 into ATRACT.

Useful database variables and OS equates

APPMHI $000E,2 (14): lower limit for screen region

ATRACT $004D (77): attract mode timer and flag

LMARGN $0052 (82): left margin

RMARGN $0053 (83): right margin

ROWCRS $0054 (84): horizontal cursor position

COLCRS $0055,2 (85): vertical cursor position

DINDEX $0057 (87): current graphics mode

SAVMSC $0058,2 (88): starting address of display buffer

OLDROW $005A (90): previous cursor position

OLDCOL $005B,2 (91): " " "

OLDCHR $005D (93): character currently at the text cursor

OLDADR $005E,2 (94): memory address of cursor

RAMTOP $006A (106): end-of-RAM + 1 (MSB only)

SDLSTL $0230,2 (560): shadow register of display list address

TXTROW $0290 (656): text window cursor position

TXTCOL $0291,2 (657): " " " "

TXTMSC $0294,2 (660): starting address of text window data buffer

RAMSIZ $02E4 (740): permanent end-of-RAM + 1 (MSB only)

CRSINH $02F0 (752): cursor inhibit, 1 = no cursor

FILDAT $02FD (765): color data for fill

DSPFLG $02FE (766): if >0 screen control codes are displayed as

ATASCII characters (EOL is uneffected)

SSFLAG $02FF (767): > 0 = stop screen print

COLPM0 $D012 (53266): actual color registers

COLPM1 $D013 (53267): loaded from shadow

COLPM2 $D014 (53268): registers during

COLPM3 $D015 (53269): vertical blank

COLPF0 $D016 (53270):

COLPF1 $D017 (53271): see above

COLPF2 $D018 (53272): for use

COLPF3 $D019 (53273):

COLBK $D020 (53274):

OS shadow registers

PCOLR0 $02C0 (704): COLPM0

PCOLR1 $02C1 (705): COLPM1

PCOLR2 $02C2 (706): COLPM2

PCOLR3 $02C3 (707): COLPM3

COLOR0 $02C4 (708): COLPF0

COLOR1 $02C5 (709): COLPF1

COLOR2 $02C6 (710): COLPF2

COLOR3 $02C7 (711): COLPF3

COLOR4 $02C8 (712): COLBK

THE RESIDENT DISK HANDLER

The resident disk handler is separate from DOS and is part of the

permanent operating system ROM. The disk handler does not use CIO.

The resident disk handler works with one sector at a time. It is used

by setting the drive number, sector number, and operation code in the

device control block. The program then jumps (JSR) to the handler

entry vector, DSKINV [$E453 (58451)].

Device control block (for resident disk handler)

DDEVIC [$0300 (768)]

Serial bus I.D. Set by handler

DUNIT [$0301 (769)]

Drive number

DCOMND [$0302 (770)]

Command byte

DSTATS [$0303 (771)]

status byte

DBUFLO [$0304 (772)]

DBUFHI [$0305 (773)]

Pointer to 128 byte memory block for data storage.

DTIMLO [$0306 (774)]

Timeout value (response time limit) in seconds

DBYTLO [$0308 (776)]

DBYTHI [$0309 (777)]

number of bytes transferred, set by handler

DAUX1 [$030A (778)]

DAUX2 [$030B (779)]

sector number

DISK HANDLER COMMANDS

GET SECTOR

Before the JSR to DSKINV is made the following parameters are set.

GET SECTOR parameters

DCOMND = $52 (82)

DUNIT = (1 - 4)

DBUFHI

and

DBUFLO = address of 128 byte buffer

DAUX1

and

DAUX2 = Sector number (LSB,MSB)

This operation will read the specified sector and put the data into

the specified buffer.

PUT SECTOR

PUT SECTOR is used the same as GET SECTOR except for DCOMND.

PUT SECTOR parameters

DCOMND = $50 (80)

This operation sends the data in the specified buffer to the specified

disk sector.

PUT SECTOR WITH VERIFY

PUT SECTOR WITH VERIFY is used the same as PUT SECTOR except for

DCOMND.

PUT SECTOR WITH VERIFY parameters

DCOMND = $57 (87)

This operation sends the data in the specified buffer to the specified

disk sector then checks for errors.

GET STATUS

Only the DUNIT and DCOMND need to be set

GET STATUS parameters

DCOMND = $53 (83)

DUNIT = (1 - 4)

The status information will be put in three bytes starting at DVSTAT

[$02EA (746)].

Status format

7 6 5 4 3 2 1 0

-----------------

DVSTAT + 0 | command stat |

-----------------

+ 1 | hardware stat |

-----------------

+ 2 | timeout value |

-----------------

The command status byte gives the following information.

Bit

0 1 = invalid command frame received

1 1 = invalid data frame received

2 1 = unsuccessful PUT operation

3 1 = disk is write protected

4 1 = active/standby

The hardware status byte contains the status register of the ISN1771-1

disk controller chip.

The timeout byte contains the maximum allowable response time for the

drive in seconds.

FORMAT DISK

The handler will format then verify the the disk. The numbers of all

bad sectors (up to 63) will be put into the specified buffer followed

by two bytes of $FF.

The following parameters are set before the call.

FORMAT parameters

DCOMND = $21 (33)

DUNIT = (1 - 4)

DBUFLO

and

DBUFHI = address of bad sector list (buffer)

After the operation the status byte is set. Also, DBYTLO and DBYTHI

will contain the number of bytes of bad sector information (not

including the two $FF bytes).

Useful data base variables and OS equates

DVSTAT $02EA,3 (746): device status block, 3 bytes

DDEVIC $0300 (768): serial bus I.D.

DUNIT $0301 (769): device number

DCOMND $0302 (770): command byte

DSTATS $0303 (771): status byte

DBUFLO $0304 (772): data buffer

DBUFHI $0305 (773): pointer

DTIMLO $0306 (774): timeout value

DBYTLO $0308 (776): number of bytes transfered

DBYTHI $0309 (777):

DAUX1 $030A (778): sector

DAUX2 $030B (779): number

DSKINV $E453 (58451): disk handler entry vector

SYSTEM INTERRUPTS

There are four types of interrupts which can occur with the 6502

microprocessor:

6502 interrupts

1. chip reset

2. IRQ, interrupt request (maskable)

3. MNI (non-maskable interrupt)

4. software interrupt (BRK instruction)

CHIP RESET

On the 400/800 the chip reset occurs only upon power-up and causes the

computer to do a cold start. On later models, pressing [SYSTEM RESET]

will cause a chip reset but the computer then does a warm start. On

the 400/800, the [SYSTEM RESET] key generates a NMI interrupt.

COLD START

This is a synopsis of the cold start routine.

The warm start flag [$0008] is set to 0 (false)

If a cartridge slot contains a diagnostic cartridge, control is handed

to the cartridge.

The end of RAM is determined by trying to complement the first byte of

each 4K block of memory.

Hardware registers at $D000 - $D4FF (except $D100 - $D1FF) are

cleared.

RAM is cleared from $0008 to the top of ram.

The user program jump vector, DOSVEC [$000A] is set to point to the

black board mode (Atari logo display mode in XL/XE models).

The screen margins are set to 2 and 39

Interrupt vectors are initialized.

Bottom of free RAM pointer, MEMLO [$02E7], is set to point to $0700.

Resident CIO handlers are initialized.

If the [START] key is pressed the cassette boot request flag, CKEY

[$004A], is set.

The CIO device table is initialized.

If a cartridge is present it is initialized.

Channel 0 is opened to the screen editor. The top-of-free-RAM

pointer, MEMTOP [$02E5], is set to point below the screen region. The

computer then waits for the screen to be established before

continuing.

If the cassette boot flag is set the cassette is booted.

If there is no cartridge present or a cartridge doesn't prevent it,

the disk is booted.

The cold start flag is reset.

If there is a cartridge present, the computer jumps to the cartridge's

run vector.

If there is no cartridge present the computer jumps through the vector

DOSVEC [$000A (10)]. DOSVEC will point to either a booted program,

the memo pad routine (400/800) or the logo display routine (XL/XE).

WARM START

The warm start flag is set to $7F (true).

cold start steps 2 - 4 are executed.

RAM is cleared from $0010 - $007F and $0200 - $03FF.

Cold start steps 7 - 14 are executed.

If cassette booted software is present the computer JSRs through

CASINI [$0002].

If disk booted software is present the computer JSRs through DOSINI

[$000C (12)].

The difference between cold start and warm start is the condition of

the warm start flag, WARMST, [$0008]. If this flag is 0 a complete

cold start is executed. If the flag is anything other than 0 then

only the warm start part of the warm start/cold start code is

executed.

NON-MASKABLE INTERRUPTS (NMI)

NMI interrupts are generated by the following conditions:

1. Display list interrupt, generated by the ANTIC chip.

2. TV vertical blank interrupt, generated by the ANTIC

chip.

3. [SYSTEM RESET] key (400/800).

When an NMI interrupt occurs, the hardware register NMIST [$D40F] is

examined to determine what type of interrupt occurred. The computer

is then directed through the proper ram vector to service the

interrupt.

DISPLAY LIST INTERRUPTS (DLIs)

The computer makes no use of DLIs. The ram vector points to an RTI

instruction.

VERTICAL BLANK INTERRUPTS (VBIs)

There are two stages to the VBI service routine. The second stage is

only done if a critical function was not interrupted.

Stage 1 (VBI)

The real time clock, RTCLOK [$0012 - $0014], is incremented.

The attract mode variables are processed.

System timer 1 is decremented. If it goes to zero the computer JSRs

through system time-out vector 1.

Stage 2 (VBI)

The hardware registers are loaded with the data in their shadow

registers.

System timer 2 is decremented. If it goes to zero the computer JSRs

through the system time-out vector 2.

System timers 3, 4, and 5 are decremented. If a timer goes to zero

the computer sets system timer flags 3, 4, and/or 5.

If auto-repeat is active, the auto-repeat process is done.

The keyboard debounce timer is decremented if not 0.

Information at the controller port registers is read, processed and

placed in the proper shadow registers.

[SYSTEM RESET] INTERRUPT

If a [SYSTEM RESET] interrupt is generated on the 400/800 the computer

jumps to the warm start routine.

INTERRUPT REQUESTS (maskable interrupts (IRQs))

When an IRQ interrupt occurs the hardware register IRQST [$D20E], the

PIA status registers, PACTL [$D302] and PBCTL [$D303] are examined to

determine what caused the interrupt.

For each interrupt, the 6502 accumulator is pushed to the stack. The

computer is then directed to the proper ram vector to service the

interrupt.

SOFTWARE INTERRUPT (BRK instruction)

The operating system doesn't use software interrupts. The software

interrupt vector points to a PLA followed by an RTI.

Interrupt vectors

Label address type function

VDSLST $0200 NMI DLI Points to an RTI

VVBLKI $0222 NMI stage 1 VBI

VVBLKD $0224 NMI return-from-interrupt routine

CDTMA1 $0226 NMI time-out 1 (used by SIO)

CDTMA2 $0228 NMI time-out 2 (not used by OS)

VPRCED $0202 IRQ not used (points to PLA,RTI)

VINTER $0204 IRQ not used (PLA,RTI)

VKEYBD $0208 IRQ keyboard interrupt

VSERIN $020A IRQ used by Serial I/O routine

VSEROR $020C IRQ used by SIO

VSEROC $020E IRQ used by SIO

VTIMR1 $0210 IRQ not used by OS (PLA,RTI)

VTIMR2 $0212 IRQ not used by OS (PLA,RTI)

VTIMR4 $0214 IRQ ?

VIMIRQ $0216 IRQ main IRQ code

VBREAK $0206 BRK unused by OS (PLA,RTI)

SYSTEM TIMERS

The following timers are updated during vertical blank (VBI) as noted

above. If a timer is decremented to 0 the computer jumps through it's

associated vector or sets it's associated flag.

Label address flag/vector

RTCLOK $0012 3 byte clock ($0012 = MSB)

CDTMV1 $0218 CDTMA1 $0226 vector (SIO time-out)

CDTMV2 $021A CDTMA2 $0228 vector

CDTMV3 $021C CDTMF3 $022A flag

CDTMV4 $021E CDTMF4 $022C flag

CDTMV5 $0220 CDTMF5 $022E flag

HARDWARE INTERRUPT CONTROL

There are two registers on the antic chip which control interrupts.

These registers can be used to disable interrupts if necessary. There

are also two associated interrupt status registers.

The IRQ enable and status registers use the same address. The result

is that reading the register does not reveal the enabled interrupts

but the interrupts pending. IRQ interrupt enable data should usually

be written to the OS shadow first. Reading the OS shadow tells which

interrupts are enabled.

Non maskable interrupt enable

NMIEN $D40E

7 6 5 4 3 2 1 0

-----------------

| | | not used |

-----------------

bit 7 1 = DLI enabled

6 1 = VBI enabled

Non maskable interrupt status

NMIST $D40F

7 6 5 4 3 2 1 0

-----------------

-----------------

bit 7 1 = DLI pending

6 1 = VBI pending

5 1 = [SYSTEM RESET] key pending

Interrupt request enable

IRQEN $D20E

7 6 5 4 3 2 1 0

-----------------

| | | | | | | | |

-----------------

bit 7 1 = [BREAK] key interrupt enable

6 1 = keyboard interrupt enable

5 1 = serial input interrupt enable

4 1 = serial output interrupt enable

3 1 = serial output-finished interrupt enable

2 1 = timer 4 interrupt enable

1 1 = timer 2 interrupt enable

0 1 = timer 1 interrupt enable

IRQEN has a shadow register, POKMSK [$0010 (A)].

Interrupt request status

IRQST $D20E

7 6 5 4 3 2 1 0

-----------------

| | | | | | | | |

-----------------

bit 7 1 = [BREAK] key interrupt pending

6 1 = keyboard interrupt pending

5 1 = serial input interrupt pending

4 1 = serial output interrupt pending

3 1 = serial output-finished interrupt pending

2 1 = timer 4 interrupt pending

1 1 = timer 2 interrupt pending

0 1 = timer 1 interrupt pending

WAIT FOR HORIZONTAL SYNC

Writing any number to WSYNC [$D40A (54282)] will cause the computer to

stop and wait for the next TV horizontal sync.

It is wise to use DLIs one TV line before needed then writing to

WSYNC. This will keep other interrupts from causing DLIs to be

serviced late. This can cause a DLI to change something in the middle

of a scan line.

Useful database variables and OS equates

POKMSK $0010 (16): IRQEN shadow

IRQEN $D20E (53774): enables IRQs when written to

IRQST $D20E (53774); gives IRQs waiting when read

PACTL $D302 (54018): bit 7 (read) peripheral A interrupt status

bit 0 (write) peripheral A interrupt enable

PBCTL $D303 (54019): bit 7 (read) peripheral B interrupt status

bit 0 (write) peripheral B interrupt enable

WSYNC $D40A (54282): wait for horizontal sync

NMIEN $D40E (54286): NMI enable

NMIST $D40F (54287): NMI status

THE FLOATING POINT ARITHMETIC PACKAGE

The routines which do floating point arithmetic are a part of the

operating system ROM. The Atari computer uses the 6502's decimal math

mode. This mode uses numbers represented in packed Binary Coded

Decimal (BCD). This means that each byte of a floating point number

holds two decimal digits. The actual method of representing a full

number is complicated and probably not very important to a programmer.

However, for those with the knowledge to use it, the format is given

below.

Floating point number representation

byte 0 xx excess 64 exponent + sign

xx \

xx > 10 BCD digits

xx /

byte 7 xx /

The decimal point is shifted to left of the MSD and the exponent is

adjusted accordingly. Therefore, the decimal point doesn't need to be

represented.

For programming purposes, floating point numbers can be in ASCII code.

It takes up to 14 bytes to store a floating point number in this

manner. The floating point package has a routine to convert numbers

between ASCII and floating point.

USE OF THE FLOATING POINT PACKAGE

The floating point package has several routines to convert between

ASCII and FP and to do the arithmetic functions. These are the

important data base variables.

Floating point data base variables

FR0 $00D4,6 (212): 6 byte buffer for floating point number

FR1 $00E0,6 (224): 6 byte buffer for floating point number

CIX $00F2 (242): index for INBUFF address

INBUFF $00F3,2 (243): 2 byte pointer to ASCII floating point number

FLPTR $00FC,2 (252): 2 byte pointer to user buffer for floating

point number

LBUFF $0580,? (1408): result buffer for FASC routine

MAKING THE CALL

To do a floating point function, first set the proper pointers and JSR

to the operation entry point. Below is a list of the entry points and

parameters.

ASCII to floating point

Converts ASCII representation pointed to by INBUFF to FP in FR0.

AFP = $D800

INBUFF = address of ASCII number

CIX = buffer offset if any

JSR AFP

FLOATING POINT TO ASCII

Converts floating Point number in FR0 to ASCII. The result will be

in LBUFF. INBUFF will point to the ASCII number which will have the

bit 7 of the last byte set to 1.

FASC = $D8E6

JSR FASC

INTEGER TO FLOATING POINT CONVERSION.

Converts a 2 byte unsigned integer (0 to 65535) in FR0 to floating

point in FR0.

IFP = $D9AA

JSR IFP

FLOATING POINT TO INTEGER CONVERSION.

Converts floating point number in FR0 to 2 byte integer in FR0.

FPI = $D9D2

JSR FPI

BCS overflow

ADDITION

Adds floating point numbers in FR0 and FR1 with result in FR0.

FADD = $DA66

JSR FADD

BCS out of range

SUBTRACTION

subtracts FR1 from FR0 with the result in FR0.

FSUB = $DA60

JSR FSUB

BCS out of range

MULTIPLICATION

Multiplies FR0 by FR1 with the result in FR0.

FMUL = $DADB

JSR FMUL

BCS out of range

DIVISION

Divides FR0 by FR1 with result in FR0.

FDIV = $DB28

JSR FDIV

BCS out of range or divisor is 0

LOGARITHMS

Puts logarithm of FR0 in FR0

LOG = $DECD

LOG10 = $DED1

JSR LOG ;for natural log.

JSR LOG10 ;for base 10 log.

BCS negative number or overflow

EXPONENTIATION

Put exponentiation of FR0 in FR0

EXP = $DDC0

EXP10 = $DDCC

JSR EXP ;for e ** Z

JSR EXP10 ;for 10 ** Z

POLYNOMIAL EVALUATION

Puts the result of an n degree polynomial evaluation of FR0 in FR0.

PLYEVL = $DD40

LDX LSB of pointer to list of floating point

coefficients, ordered high to low.

LDY MSB of above

LDA number of coefficients in list

JSR PLYEVL

BCS overflow

CLEAR FR0

Sets FR0 to all zeroes

ZFR0 = $DA44

JSR ZFR0

CLEAR ZERO PAGE FLOATING POINT NUMBER

Clears user floating point number in page zero.

ZF1 = $DA46

LDX address of zero page FP buffer

JSR ZF1

LOAD FR0 WITH FLOATING POINT NUMBER

Loads FR0 with user FP number in buffer pointed to by 6502 X and Y

registers or by FLPTR. After either operation below, FLPTR will point

to the user FP buffer.

FLD0R = $DD89

LDX lsb of pointer

LDY msb

JSR FLD0R

FLD0P = $DD8D

FLPTR = address of FP number

JSR FLD0P

LOAD FR1 WITH FLOATING POINT NUMBER

Loads FR1 with user FP number in buffer pointed to by 6502 X and Y

registers or by FLPTR. After either operation below, FLPTR will point

to the user FP buffer.

FLD1R = $DD98

LDX lsb of pointer

LDY msb

JSR FLD1R

FLD1P = $DD9C

FLPTR = address of FP number

JSR FLD1P

STORE FR0 IN USER BUFFER

stores the contents of FR0 in user FP buffer pointed to by 6502 X and

Y registers or by FLPTR. After either operation below, FLPTR will

point to the user FP buffer.

FST0R = $DDA7

LDX lsb of pointer

LDY msb

JSR FST0R

FST0P = $DDAB

FLPTR = address of FP number

JSR FST0P

MOVE FR0 TO FR1

Moves the contents of FR0 to FR1

FMOVE = $DDB6

JSR FMOVE

The usual use sequence of the floating point package might be to:

load FR0 and FR1 with FP numbes from user specified buffers

do the math

then store FR0 in a user buffer.

An alternative might be to:

convert an ASCII representation to FP (the result is automatically in

FR0).

move FR0 to FR1.

Convert the second ASCII number.

Do the math.

Convert FR0 back to ASCII.

Store the number back into a user buffer.

The floating point package uses the following blocks of RAM.

RAM used by floating point package

$00D4 - $00FF

$057E - $05FF

If the floating point package is not used the above ram is free.

Useful data base variables and OS equates

FR0 $00D4,6 (212): system FP buffer

FR1 $00E0,6 (224): system FP buffer

CIX $00F2 (242): INBUFF index

INBUFF $00F3,2 (243): pointer to ASCII FP buffer

FLPTR $00FC,2 (252): pointer to user FP buffer

LBUFF $0580 (1408): result buffer for FP to ASCII

AFP $D800 (55296): ASCII to FP

FASC $D8E6 (55526): FP to ASCII

IFP $D9AA (55722): integer to FP

FPI $D9D2 (55762): FP to integer

ZFR0 $DA44 (55876): clear FR0

ZF1 $DA46 (55878): clear zero page FP buffer

FSUB $DA60 (55904): FR0 - FR1

FADD $DA66 (55910): FR0 + FR1

FMUL $DADB (56027): FR0 * FR1

FDIV $DB28 (56104): FR0 / FR1

FLD0R $DD89 (56713): load FR0 by X,Y pointer

FLD0P $DD8D (56717): load FR0 by FLPTR pointer

FLD1R $DD98 (56728): load FR1 by X,Y pointer

FLD1P $DD9C (56732): load FR1 by FLPTR pointer

FST0R $DDA7 (56743): store FR0 at buffer by X,Y pointer

FST1P $DDAB (56747): store FR0 at buffer by FLPTR pointer

FMOVE $DDB6 (56758): move FR0 to FR1

EXP $DDC0 (56768): e exponentiation

EXP10 $DDCC (56780): base 10 exponentiation

PLYEVL $DD40 (56640): polynomial evaluation

LOG $DECD (57037): natural log of FR0

LOG10 $DED1 (57041): base 10 log of FR0

Boot software formats

There are three ways which programs may be booted (loaded

automatically upon power-up):

From the disk drive

From the cassette recorder

From a ROM cartridge

DISK BOOTED SOFTWARE

The disk drive is the primary source for programs (other than the

BASIC interpreter in the computer ROM). A program booted from disk

must be a machine language program. Secondly, the program is arranged

on disk in a different manner from the DOS files.

When the computer is first turned on, it will attempt to read a

program starting at sector one in disk drive one. The exceptions are,

if a cartridge prevents the disk boot process or the [START] key is

pressed. The program is expected to use all 128 bytes of each

sector.

FORMAT OF A DISK BOOTED PROGRAM

A disk booted program begins at sector one on the disk and continues

in sequence. The first six bytes of the first sector contain program

information. The rest of the bytes contain the program itself.

Disk boot program header

1st byte $00 flags, stored in DFLAGS [$0240]

$xx number of sectors used by program

$xx address to start load

$xx

$xx initialization address

6th byte $xx

7th byte $xx start of program

The flags byte is usually unused and should be zero.

The load address is stored in BOOTAD [$0242,2 (578)].

The initialization address is stored in DOSINI [$000C,2 (12)].

After the program is completely loaded the computer will JSR to the

address stored in DOSINI for initialization. It will then jump to the

address stored in DOSVEC to run the program.

The initialization part of the program should set the

bottom-of-free-RAM pointer, MEMLO [$02E7,2 (743)], to point to the end

of the program + 1. This will protect the program from the computer

and other programs. The top-of-user-RAM pointer, APPMHI [$000E,2

(14)], is also usually set to point to the same address. This will

protect the program from the video hardware. It must also set DOSVEC

[$000A,2 (10)] to actually point to the run address of the program.

The initialization should of course end with and RTS. With DOSINI and

DOSVEC properly set, the program will restart up pressing the [SYSTEM

RESET] key.

Rmember that the load address of the program should be six bytes

before where you want the program to reside in memory. The six byte

header will load at the specified start address followed by the

program.

CASSETTE BOOTED SOFTWARE

The cassette boot process is nearly identical to the disk boot

process. The processes are so similar that cassette boot programs can

usually be transferred directly to disk and vice-versa. The two

differences are:

The cassette is booted instead of the disk if the [START] key is

pressed when the power is turned on.

A bug in early operating systems requires the booted program to turn

off the cassette motor with the following command.

LDA #$3C

STA PACTL [$D302]

CARTRIDGE BOOTED SOFTWARE

The Atari 800 has two cartridge slots. All other models have only

one. The second cartridge slot, slot B on the 800, resides from $8000

to $9FFF. The first slot, slot A, resides from $A000 to BFFF. If a

cartridge is inserted in a slot it will disable any RAM in the same

area.

Slot A, which is present in all models, can reside at the entire 16K

used by both cartridges in the 800 ($8000 to $BFFF).

Cartridges use the last six bytes for boot information. In cartridge

A these bytes are from $BFFA to $BFFF. In cartridge B they are from

$9FFA to 9FFF.

last six bytes of a cartridge

$9FFA or $BFFA xx start address

xx flag byte

xx init address

$9FFF or $BFFF xx

Flag byte

bit 0 1 = allow disk boot

bit 2 0 = do not start cartridge after init

bit 7 1 = cartridge takes control before OS is

initialized

The initialization process for the cartridge should be similar to that

for disk and cassette. A minimum of an RTS instruction is required.

The third byte of the cartridge tailer is used by the OS to check for

the presence of a cartridge. This byte must be zero.

A 16K cartridge will use both cartridge areas and the cartridge B

tailer area can be used for program code.

THE CARTRIDGE HARDWARE

Most cartridges consist of two ROM chips on a single circuit board.

Moreover, both chip sockets have identical pin assignments. In other

words, the chips can be switched to opposite sockets and the

cartridge will still work. The difference is in the chips themselves.

On one chip, the A12 pin acts as an active-low chip select. On the

other the A12 pin acts as an active-high chip select. Therefore the

state of the A12 pin selects between the two chips.

Cartridge slot pin assignments

BACK

111111

543210987654321

---------------

SRPNMLKJHFEDCBA

FRONT

1 1 = 16K A A13 (16K only)

2 A3 B GND

3 A2 C A4

4 A1 D A5

5 A0 E A6

6 D4 F A7

7 D5 H A8

8 D8 J A9 __

9 D1 K A12 (CS)/(CS)

10 D0 L D3

11 D6 __ M D7

12 (CS) N A11

13 +Vcc P A10

14 +Vcc R NC

15 NC S NC

The BASIC interpreter resides in the memory used by cartridge A. In

400, 800 and 1200XL models, a BASIC cartridge is required to run BASIC

programs. On other XL and XE models, inserting a cartridge into the

slot or pressing the [OPTION] key upon power-up will disable the

internal BASIC ROM. If BASIC is disabled without inserting another

cartridge, the area from $A000 to $BFFF will contain RAM.

Useful data base variables and OS equates

APPMHI $000E,2 (14): low limit of screen region

DOSVEC $000A,2 (10): run and program reset vector

DOSINI $000C,2 (12): init and reset init

CARTB $8000 (32768): start of cartridge B

CARTA $A000 (40960): start of cartridge A

PACTL $D302 (54018): port A control register Bit 3

controls the cassette motor

THE SERIAL INPUT/OUTPUT INTERFACE (SIO)

Most input and output with the Atari computer passes through the

serial I/O bus. The SIO interface is rather complicated but you are

unlikely to need to use it directly. CIO usually handles SIO for you.

However, if hardwareyou want to design your own I/O device and it's associated

handler, you need to know how to use the SIO.

SIO transfers data at a rate of 19,200 baud on separate input and

output lines. The data is sent one byte at a time, LSB first, in an

asynchronous format. There are also clock-in and clock-out lines.

There is a signal on the clock-out line but it is not used by any

present devices. The clock-in line is available for synchronous

transfer but is not used by the OS. The signal on the clock-out line

goes high at the leading edge of each bit and goes low in the middle

of each bit.

One byte of SIO data

+-+ +-+ +-+ +-+ +-+ +-+ +-+ +-+

-------------+ +-+ +-+ +-+ +-+ +-+ +-+ +-+ +------

---------+ +---+ +-------+ +--------

| 0 | 1 | 0 | 1 1 | 0 0 | 1 data

+-------+ +---+ +-------+

| |

start bit stop bit

The SIO interface is used much like the resident disk handler. In

fact, it uses the same device control block as the resident disk

handler. After the control block parameters are set, a JSR is made to

the SIO entry vector, SIOV, at $E459 (58457).

Device control block (for SIO)

DDEVIC [$0300 (768)]

Serial bus I.D. Set by handler or program.

DUNIT [$0301 (769)]

Device number if more than one.

DCOMND [$0302 (770)]

Device command byte.

DSTATS [$0303 (771)]

Before the SIO call, this byte tells whether the operation is read,

write or that there is no data transfer associated with the command.

After the call this byte will hold the status (error/no error code) of

the operation.

DSTATS format before command

7 6 5 4 3 2 1 0

-----------------

|W|R| not used |

-----------------

If both W and R are 0, there is no data transfer.

DBUFLO [$0304 (772)]

DBUFHI [$0305 (773)]

Points to the data buffer for either input or output.

DTIMLO [$0306 (774)]

Timeout value (response time limit) in 64/60ths of a second to be set

by handler or program.

DBYTLO [$0308 (776)]

DBYTHI [$0309 (777)]

Number of bytes to be transferred, set by handler or program. This

parameter is not required if the DSTATS specifies no data transfer.

DAUX1 [$030A (778)]

DAUX2 [$030B (779)]

These parameters are sent to the device as part of the command frame.

USING THE SIO INTERFACE

All commands on the serial bus must originate from the computer. The

peripherals will present data on the bus only when commanded to do

so.

Any operation on the serial bus begins with a five byte command frame.

While the command frame is being sent, the command line of the serial

connector is 0.

Command frame format

$xx DDEVIC

$xx DCOMND

$xx DAUX1

$xx DAUX2

$xx checksum

The first four bytes of the command frame come from the device control

block. the checksum is the sum of the other four bytes with the carry

added back after each addition.

If both R and W of the DSTATS are 0, no data is sent to, or expected

from the peripheral, after a command frame is sent. However, the

device is usually expected to send an ACK byte ($41) after the command

frame is sent. If the command frame is invalid, an NAK byte ($4E)

should be sent.

If the operation is output (W = 1) the computer will send a data frame

after it receives the ACK of the command frame. It then expects an

ACK after the data frame is sent.

If the operation is an input (R = 1) the computer expects a data frame

from the peripheral after the ACK. With either input or output, a

"complete" code ($43) should be sent to the computer when the

operation is finished. The "complete" code would follow the ACK of

the data frame with an output operation.

If the operation is not completed for some reason, the peripheral

should send an error code ($45) instead of "complete".

SIO data frame

byte 1 $xx\

> data bytes

byte n $xx/

byte n+1 $xx checksum

SIO commands

READ $52

WRITE $57

STATUS $53

PUT $50

FORMAT $21

DOWNLOAD $20

READADDR $54

READ SPIN $51

MOTOR ON $55

VERIFY

SECTOR $56

Present SIO device I.D.s

DISK $31 - $34 (D1 - D4)

PRINTER $40

RS-232-C $50 - $53 (R1 - R4)

THE SERIAL CONNECTOR

The serial connectors on the computer and all peripherials are

identical. Nearly all peripherials have two serial connectors.

Either connector may be used for any connection. The serial bus is

designed so that peripherials can be daisy-chained together. The

following is a diagram of the serial connector.

The serial connector pin-out

1 1

2 4 6 8 0 2

-----------

/o o o o o o\

/o o o o o o o\

-----------------

1 3 5 7 9 1 1

1 3

1 clock in (to computer)

2 clock out

3 data in

4 GND

5 data out

6 GND

7 command (active low)

8 cassette motor control

9 proceed (active low)

10 +5V/ready

11 audio in

12 +12V (400/800)

13 interrupt (active low)

Proceed goes to pin 40 (CA1) of the PIA. It is not used by present

peripherials.

Interrupt goes to pin 18 (CB1) of the PIA. It is not used by present

peripherials.

Pin 10 doubles as a 50mA +5V peripharal power supply and a computer

ready signal.

Useful database variables and OS equates

SIOV $E459 (58457): serial port handler entry

DDEVIC $0300 (768): device ID

DUNIT $0301 (769): device number

DCOMND $0302 (770): command byte

DSTATS $0303 (771): status byte

DBUFLO $0304 (772): data buffer pointer

DBUFHI $0305 (773):

DTIMLO $0306 (774): timout value

DBYTLO $0308 (776): number of bytes to transfer

DBYTHI $0309 (777):

DAUX1 $030A (778): sent to device

DAUX2 $030B (779): sent to device

THE HARDWARE CHIPS

The previous chapters described the operating system of the computer.

The following chapters will examine the hardware which supports the

6502 and the hardware's associated software.

THE GTIA CHIP

The GTIA (George's Television Interface Adapter) is the main video

circuit in the computer. It controls the following functions.

GTIA functions

Priority of overlapping objects

Color and brightness, including information from the antic chip.

Player/missile control.

console switches and game control triggers.

THE ANTIC CHIP

The main job of the ANTIC chip is interpreting the display buffer for

the GTIA chip. The ANTIC chip is somewhat of a processor in it's own

right. The program which runs it is called the display list and

usually resides just before the display buffer in memory.

The ANTIC chip operates independent of the 6502. It operates by

direct memory access (DMA). The ANTIC chip gives a HALT signal the

6502, causing the 6502 to give up control of the address bus. The

ANTIC chip can then read any data it needs to from memory.

ANTIC chip functions

DMA (Direct Memory Access) control.

NMI (Non-Maskable Interrupt) control.

LIGHT PEN READING

WSYNC (wait for horizontal sync)

THE POKEY CHIP

The most important jobs of the POKEY chip are reading the keyboard and

operating the serial port. It also has the following functions.

POKEY chip functions

Keyboard reading.

Serial port.

Pot (game paddles) reading.

Sound generation.

System timers.

IRQ (maskable interrupt) control.

Random number generator.

THE PIA CHIP

The PIA (Parallel Interface Adapter) is a commonly used I/O chip. It

consists of two 8 bit parallel ports with hand shaking lines. In the

Atari, it has the following functions.

Game controller port control (bi-directional).

Peripheral control and interrupt lines.

Registers in the hardware chips are treated as memory addresses. Many

of the registers are write only. These registers cannot be read from

after they are written to. Other registers control one function when

written to and give the status of an entirely different function when

read from. Still other registers are strobes. Any command which

causes the address of one of these registers to appear on the address

bus will cause their functions to be performed.

The write only registers have shadow registers in RAM. Data to be put

in the registers is usually put into the shadow registers. The data

in the shadow registers is automatically moved to the operating

registers during vertical blank.

For register use and address, see the previous chaptes on the

associated functions.

DISPLAY LISTS

[some of this file was lost...]

chip also has a memory scan counter. This register scans the display

buffer for data to be interpreted and displayed. Once loaded, the

memory scan counter's 4 most significant bits are fixed. The result

is that the memory scan counter cannot cross a 4K memory boundary

(i.e. $AFFF to $B000) without being reloaded.

DISPLAY LIST INSTRUCTIONS

There are three basic instructions in the display list. The type of

instruction is determined by bits 0,1,2 and 3 of an instruction byte.

The other four bits give auxilliary parameters for the instruction.

Bit 7 always enables a display list interrupts (DLIs).

Display list instruction format

7 6 5 4 3 2 1 0

-----------------

|I|n|n|n|0|0|0|0|

-----------------

\ / \ /

--- ------

| |

| 0 = display blank lines

0-7 = number of blank lines (1-8)

7 6 5 4 3 2 1 0

-----------------

|I|W| | |0|0|0|1|

-----------------

| \ /

| ------

| |

| 1 = jump (3 byte instruction)

0 = jump and display one blank line

1 = jump and wait for vertical blank

7 6 5 4 3 2 1 0

-----------------

|I|R|H|V|M|M|M|M|

-----------------

| | | | \ /

| | | | ------

| | | | |

| | | | 2-F = display one line of graphics in

| | | | ANTIC mode 2-F

| | | 1 = horizontal scroll enabled

| | |

| | 1 = vertical scroll enabled

| |

| 1 = reload memory scan counter with next two bytes

1 = display list interrupt, all instructions

In the display instruction, the ANTIC mode is different from the CIO

graphics mode. However, each CIO graphics mode uses a particular

ANTIC mode. Below are descriptions of the ANTIC modes with their

associated graphics (CIO) modes.

ANTIC MODE 2 (Graphics 0)

Uses 8 pixel by 8 pixel characters, 40 characters horizontal, 8 TV

scan lines vertical. Only one color can be displayed at a time.

ANTIC MODE 3

8 X 10 pixel, Graphics 0 type characters. This mode requires a custom

character set. The advantage is that it allows true decenders. The

custom C-set is still 8 X 8 pixels. Lower-case letters with decenders

have the bottom row of pixels put on the top row.

Lower-case "y" for ANTIC mode 3

C-set Display

---------- ----------

| XXXXX | | |

| | | |

| XX XX | | XX XX |

| XXXXX | | XXXXX |

| XX | | XX |

---------- | XXXXX |

| |

----------

ANTIC MODE 4 (graphics 12 on XL and XE)

This mode has characters the same size as graphics 0. However, the

characters are only 4 X 8 pixels. This gives only half the horizontal

resolution of graphics 0. The advantage is that up to four colors of

"graphics 0" characters can be displayed at once. This mode also

requires a custom C-set. Below is a comparison of the normal C-set to

one which works with the ANTIC 4 mode.

Upper-case "A" for ANTIC modes 2 and 4

mode 2 mode 4

---------- ----------

| | | |

| XX | | yy |

| XXXX | | yy |

| XX XX | |xx zz |

| XXXXXX | |xxyyzz |

| XX XX | |xx zz |

| | | |

---------- ----------

xx, yy and zz represent two bit binary numbers, controlling one pixel

each. These numbers determine which color register a pixel is

assigned to: (COLOR0, COLOR1, COLOR2 or COLOR3).

ANTIC mode 5

Antic mode five is identical to ANTIC mode 4 except the characters are

displayed twice as tall. This makes only 12 lines on the screen.

ANTIC MODE 6 (Graphics 1)

This mode uses 8 X 8 pixel characters except they are displayed twice

as wide as in ANTIC mode 2. There are 3 colors available at once but

only one case (upper or lower) can be displayed at a time. The data

base variable CHBAS [$02F4 (756)] controls the character, [$E0 (224) =

upper-case, $E2 (226) = lower-case]

The color/character is controlled by either the color statement or the

ATASCII number of the character printed. Control characters are

controlled by COLOR0, upper-case characters by COLOR1 and lower-case

characters by COLOR2. Remember that all characters print as

upper-case alpha characters, but of different colors.

ANTIC MODE 7 (Graphics 2)

This mode is identical to mode 6 except the characters are displayed

twice as tall. This results in only 12 lines possible on the screen.

ANTIC MODE 8 (Graphics 3)

This is the first graphics (non-character) mode. This mode, as other

non-character graphics modes do, uses data in the display buffer as a

bit map to be displayed.

A command to display in mode 8 will cause the ANTIC chip to read the

next 10 bytes in the display buffer. Each pair of bits will control

one pixel as in mode 4. However, the pixels are blocks the same size

as a Graphics 0 (ANTIC 2) characters.

ANTIC MODE 9 (Graphics 4)

This is similar to ANTIC mode 8 except each byte controls 8 pixels

(instead of 4) and only one color can be displayed at a time. The

pixels are also half the size of those in ANTIC mode 8.

ANTIC MODE A (Graphics 5)

This mode uses 20 bytes per line/command. As in ANTIC mode 8, each

pair of bits controls one pixel. The result is that the pixels are

the same size as in ANTIC mode 9 but four colors can be displayed at

once.

ANTIC MODE B (Graphics 6)

As in mode A, there are 8 pixels per byte and only one color. The

pixels are half the size as in mode A.

ANTIC MODE C

Like mode B except the pixels are half as tall (only one T.V. line).

ANTIC MODE D (Graphics 7)

40 Bytes per line, each byte controls 4 pixels. The pixels are 1/4 as

large as in ANTIC mode 8 (Graphics 3).

ANTIC MODE E (Graphics 15 on XL and XE)

Like mode D except the pixels are half as tall (one T.V. line). Antic

mode E is sometimes called Graphics 7.5

ANTIC mode F (Graphics 8, 9, 10 and 11)

This is the highest resolution mode. Pixels are 1/8 the size of ANTIC

mode 8 or mode 2 characters. It uses 40 bytes per line, each byte

controlling 8 pixels, unless the GTIA chip intervenes. Only one color

can be displayed at a time.

DISPLAY LIST EXAMPLES

When CIO opens a channel to the screen, it sets up the proper display

list for the ANTIC chip. The following are the things CIO must handle

when setting up the display list.

Display list duties as used by CIO

display a certain number of blank lines at the top of the screen.

Load the memory scan counter with the address of the display data

buffer.

Display the required number of lines in the required ANTIC mode.

Set up a jump instruction if the display list crosses a 1K memory

boundary.

Set up a reload-memory-scan-counter instruction if the display data

buffer crosses a 4K memory boundary.

CIO assumes that the display data buffer will butt against an 8K

memory boundary. If a program causes the display buffer to cross a 4K

boundary (by changing RAMTOP [$006A (106)] to point to an address

which is not at an 8K boundary) the screen will be scrambled. This is

not usually a problem if the graphics mode doesn't require a large

block of memory.

SAMPLE DISPLAY LIST

Below is an example of a Graphics 0 display list as CIO would set it

up.

Display list for Graphics 0

assuming BASIC starts at $A000

address instruction explanation

Dec. Hex.

$9C20 112 $70 \

112 $70 >---- 24 blank lines (8 each command)

112 $70 /

66 $42 ----- load memory scan counter with

$9C24 64 $40 \__ next two bytes and display one line

156 $9C / \ of ANTIC 2 characters

2 $02 -\ |

2 $02 | \- address of display data buffer

2 $02 |

2 $02 \--- 2nd ANTIC 2 instruction

- ---

2 $02 ----- 24th ANTIC 2 instruction

65 $41 \

32 $20 >---- jump back to start of list

156 $9C /

$9C40 ??? ?? first byte of display data buffer

--- --

$9FFF ??? ?? last byte of buffer

$A000 start of ROM

A display list for a higher resolution graphics mode would require

more instructions and might cross a 1K boundary. It would then

include a jump instruction to cross the boundary.

MULTIPLE DISPLAYS

It is possible to set up multiple displays and use one at a time. The

technique of changing from one display to another is called page

flipping. Below is the simplest way to set up two displays.

setting up two displays

Call a graphics mode through CIO or by using a BASIC GRAPHICS

command.

Store the display list pointers, SDLSTL and SDLSTH, and the CIO screen

pointer, SAVMSC [$0058,2 (88)].

Move the start-of-ROM pointer, RAMTOP [$006A (106)] to below the

current display list. RAMTOP is a one byte pointer so it changes in

increments of one page (256 bytes).

make another graphics call as in the first step.

store the new display list pointer and CIO screen pointer.

This will set up two displays, each with it's own display list. If

the displays are in the same graphics mode, or you will not make any

changes in the displays with CIO commands, (PLOT, PRINT, etc.) you can

flip between the two simply by changing the display list pointer.

If the screens are in the same graphics mode and you want to change

which one to do CIO commands to, Change the CIO screen pointer, SAVMSC

[$0058,2 (88)]. This way, you can display one screen while drawing on

the other.

If you want to do CIO commands to screens of different graphics modes,

you will have the move RAMTOP and do a graphics call to change

screens.

If your manipulation of RAMTOP causes the display data buffer to cross

a 4K boundary, the screen may be scrambled.

DISPLAY LIST INTERRUPTS

DLIs are not used by the operating system. However, other programs

can initiate and use them. Use the following steps to set up display

list interrupts.

Setting up DLIs

Set bit 7 of the display list instruction for the line before you want

the interrupt to occur. (The interrupt routine should set WSYNC and

wait for the next line to execute.)

Set bit 7 of NMIEN [$D40E (54286)] to enable DLIs.

Set the DLI routine vector, VDSLST [$0200,2 (512)] to point to your

machine language DLI routine.

Your DLI routine should set WSYNC [$D40A (54282)]. STA WSYNC will do.

THis will cause the 6502 to wait for the next horizontal sync. This

will keep the DLI routine from changing something in the middle of a

T.V. line.

The DLI routine must end with an RTI instruction.

SCROLLING

Scrolling is controlled by a combination of scroll position registers,

and changing the memory scan counter. Basically, course scrolling is

done by reloading the memory scan counter and fine scrolling is done

by changing the scroll registers.

VERTICAL SCROLLING

Vertical scrolling is very simple. Follow the steps below to set up

vertical scrolling of graphics.

Steps to use vertical scrolling

Set bit 4 of the first byte of the display list instruction for each

line to be scrolled.

Put the number of T.V. lines to offset the graphics vertically in the

vertical scroll register, VSCROL [$D405 (54277)]

The vertical scroll register can offset the graphics upward by 0 - 7

T.V. lines in the 24 line graphics modes (ANTIC modes 2 and 4). In 12

line graphics modes (ANTIC modes 5 and 7) it can vertically offset the

graphics by 0 - 15 T.V. lines. To offset the graphics an 8th (or

16th) line, the scroll register is reset to 0 and the memory scan

counter is reloaded with the address of the next line of graphics in

the display data buffer. If the entire screen is being scrolled, the

load-memory-scan-counter command (near the beginning of the display

list) is changed to point to the address of the second line of

graphics.

HORIZONTAL SCROLLING

Horizontal scrolling works much like vertical scrolling. It is

enabled by setting bit 5 of the instruction for each line to be

scrolled. The horizontal scroll register, HSCROL [$D404 (54276)],

sets the offset. The small difference is that graphics are moved

twice as far per change (two graphics 8 pixels instead of one). Also,

when HSCROL = 0 the graphics are offset beyond the left edge of the

screen by 16 color clocks (32 Graphics 8 pixels). When HSCROL = 15,

the graphics line is shifted one color clock (2 Graphics 8 pixels) to

the left of the screen.

The big difference is that the memory scan counter gets messed up.

This means that you must use a reload-memory-scan-counter command for

each line of graphics. This is a major modification of the display

list. It will require you to move and build the list yourself.

The advantage of this is that you can have a scrolling window in a

large graphics map. The technique is to move the window by reloading

the memory scan counter, then fine scrolling to the invisible bytes

beyond the edges of the screen.

useful data base variables and OS equates

SAVMSC $0058,2 (88): pointer to current screen for CIO commands

RAMTOP $006A (106): start-of-ROM pointer (MSB only)

VDSLST $0200,2 (512): DLI vector

RAMSIZ $02E4 (740): permanent start-of-ROM pointer (MSB only)

DLISTL $D402 (54274): display list pointer low byte

DLISTH $D403 (54275): " high byte

HSCROL $D404 (54276): horizontal scroll register

VSCROL $D405 (54277): vertical scroll register

NMIEN $D40E (54286): NMI enable (DLIs)

Shadow registers

SDLSTL $0230 (560): DLISTL

SDLSTH $0231 (561): DLISTH

PLAYER AND MISSILE (PM) GRAPHICS

Players and missiles (called sprites on some computers) are movable

objects which are independent of the normal graphics.

Player and missile graphics are fairly straight forward. Once the

computer is set-up for PM graphics, five 8-pixel-wide columns can be

displayed on the screen. The horizontal resolution (width of each

pixel) and the vertical resolution (number of scan lines per pixel)

are variable. The horizontal position of each column is determined by

it's horizontal position register. Each column is simply a

representation of a bit map in a certain block of memory. If you want

to draw an object on the screen, you simply put a bit map representing

it in the proper memory block. The vertical position of an object is

determined by the location of it's bit map in memory. For example, if

you want to draw a happy face in the middle of the screen, you put a

happy face bit map in the middle of one of the memory blocks

controlling one of the columns.

One column (player) displayed on the screen

---------- first byte of a block

| |

------------------------------

| | | |

| | ++++ | visible |

| | + + | |

| |+ + + +| |

| |+ +| area |

| |++ ++| |

| |+ ++++ +|--object |

| | + + | bit map |

| | ++++ | |

| | | |

------------------------------

| |

---------- last byte of a block

Horizontal positions

$00 $30 $CE $FF

(0) (48) (206) (255)

| | | |

| Left edge right edge |

| |

Far left far right

To move the happy face vertically you would move the entire bit map in

memory. To move the happy face horizontally you change the number in

the horizontal position register for the proper player.

One of the players can be (and often is) split into four columns of

two pixels wide each. These columns are then called missiles. In

this case, each missile has it's own horizontal position register.

SETTING UP PM GRAPHICS

PM graphics are enabled by the direct memory access control register,

DMACTL [$D400 (54272)]. The program using PM graphics will usually

use the shadow register, SDMCTL [$022F (559)].

DMACTL (SDMCTL)

7 6 5 4 3 2 1 0

-----------------

|0|0| control |

-----------------

bits

5 1 = enable display list reading

4 0 = one line player resolution

1 = two line player resolution

3 1 = enable four players

2 1 = enable fifth player or missiles

1 & 0 00 = no background

01 = narrow background (128 color clocks,

1 color clock equals 2 GRAPHICS 8 pixels)

10 = normal background (160 color clocks)

11 = wide background (192 color clocks)

Normally, bits 5 and 1 are set to 1. Bits 4, 3 and 2 are used to

enable players and/or missiles accordingly.

Once DMACTL is set up for the type of PM graphics to enable, the

graphics control register, GRACTL [$D01D (53277)], is used to actually

enable the PM graphics.

GRACTL

7 6 5 4 3 2 1 0

-----------------

-----------------

Bits

2 1 = latch paddle triggers

1 1 = enable four players

0 1 = enable fifth player or missiles

If only DMACTL is set up, the ANTIC chip will access memory for PM

graphics but will not display them.

Next, the memory area used for the PM bit maps must be set. This

block must start on a 2K (8 page) boundary if single line resolution

is used and a 1K (4 page) boundary for two line resolution.

The page number where the bit map starts is stored in the PM base

will be a multiple of 8. For two line resolution it will be a

multiple of 4. PMBASE holds the MSB of the address of the PM bit map.

The LSB will always be 0 so it need not be specified.

The PM bit maps

2 line resolution

128 bytes (1/2 page)

per player

----------------- start + 0

| |\

+---------------+ 1-1/2 page

| | (384 bytes)

+===============+ unused

| |/

+---------------+ +$180 (384)

|M3 |M2 |M1 |M0 | fifth player or missiles

+===============+ +$200 (512)

| player 0 map |

+---------------+ +$280 (640)

| player 1 map |

+===============+ +$300 (768)

| player 2 map |

+---------------+ +$380 (896)

| player 3 map |

+===============+ +$400 (1024)

1 line resolution

256 bytes (1 page)

per player

----------------- start + 0

| |\

+ +

| |

+===============+

| | 768 bytes

+ +

| | (3 pages)

+===============|

| | unused

+ +

| |/

+===============+ +$300 (768)

+M3 |M2 |M1 |M0 | or missiles

| | | | |

+===============+ +$400 (1024)

| |

+ player 0 map +

| |

+===============+ +$500 (1280)

| |

+ player 1 map +

| |

+===============+ +$600 (1536)

| |

+ player 2 map +

| |

+===============+ +$700 (1792)

| |

+ player 3 map +

| |

+===============+ +$800 (2048)

Example of using P/M graphics in BASIC

0 REM ---LABEL REGISTERS ETC

10 LINES=2

20 VERT=120

22 IF LINES=2 THEN VERT=VERT/2

30 PM0=1024

32 IF LINES=2 THEN PM0=PM0/2

40 HORIZ=120

50 PCOLR0=704

60 SDMCTL=559

70 SIZEP0=53256

80 HPOSP0=53248

90 SDMCTL=559

100 PMRAM=PEEK(106)-16

110 PMBASE=54279

120 GRACTL=53277

130 PMSTART=PMRAM*256+PM0

200 REM ---SET REGISTERS

210 POKE SDMCTL,62

212 IF LINES=2 THEN POKE SDMCTL,46

220 POKE SIZEP0,1

230 POKE HPOSP0,HORIZ

240 POKE PCOLR0,88

250 POKE PMBASE,PMRAM

260 POKE GRACTL,3

300 REM ---DRAW PLAYER

310 POKE PMSTART+VERT,60

320 POKE PMSTART+VERT+1,66

330 POKE PMSTART+VERT+2,165

340 POKE PMSTART+VERT+3,129

350 POKE PMSTART+VERT+4,195

360 POKE PMSTART+VERT+5,189

370 POKE PMSTART+VERT+6,66

380 POKE PMSTART+VERT+7,60

The above program will draw a happy face in about the middle of the

screen using player 0. To move the player horizontally, poke a

different number into HPOSP0. To draw the player in a different

vertical position, change VERT. To use a different player or missile,

use the memory maps above to find the starting address of the player

you want to use. For example, to use player 1 change line 40 to

PM1=1280. Then change line 130 to PMSTART=PMRAM*256+PM1. The

variable "LINES" determines the vertical resolution. The number poked

into SIZEP0 determines the width.

P/M PRIORITY

The priorities of players, missiles and non-P/M graphics can be

controlled by the PRIOR register [$D10B (53275)] and its shadow

appear to move in front of lower priority objects. The format of

PRIOR is as follows:

PRIOR bit assignment

7 6 5 4 3 2 1 0

-----------------

| | | | | | | | |

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

Bits

7-6 Control the GTIA graphics modes.

00 = normal

01 = mode 9

10 = mode 10

11 = mode 11

5 1 = multiple color player enable. Permits

overlapping of players 0 and 1 or

2 and 3 with a third color in the

overlapped region.

4 1 = fifth player enable. All missiles

will assume the color controlled by

COLOR3 [$2C7 (711)]. missiles are

positioned together to make the fifth

player.

3-0 Controls the priorities of players, missiles

and other graphics. Objects with higher priority will appear to move

in front of those with lower priority.

The following chart may need some clarification. In the chart:

PM0 = player 0 and missile 0

C0 = COLOR0, plotted graphics controlled

by color register 0 in the SETCOLOR

command.

P5 = all four missiles when combined

into one player.

BAK = the background, known as COLOR4 or color

Etc.

Bits 0-3 of PRIOR and P/M priorities

Bit 3=1 2=1 1=1 0=1

C0 C0 PM0 PM0 highest

C1 C1 PM1 PM1 priority

PM0 C2 C0 PM2

PM1 C3+P5 C1 PM3

PM2 PM0 C2 C0

PM3 PM1 C3+P5 C1

C2 PM2 PM2 C2

C3+P5 PM3 PM3 C3+P5 lowest

BAK BAK BAK BAK priority

Only one priority bit can be set at a time. If more than one priority

bit is 1, overlapping areas of conflicting priorities will turn

black.

COLLISIONS

Each player or missile has a register showing overlap (collisions)

with other objects. Each player has two registers assigned to it; one

to detect collisions with other players and one to detect collisions

with plotted objects. Likewise each missile has two registers; one to

detect collisions with players and one to detect collisions with

plotted objects. Careful use of these 16 registers can detect any

type of collision.

Each register uses only the lower 4 bits. The bits which equal 1 tell

what the associated object has collided with. For example, to detect

collisions of player 1 to other players examine P1PL [$D00D (53261)].

P1PL, player 1 to player collisions

7 6 5 4 3 2 1 0

-----------------

P1PL |unused | | | | |

-----------------

8 4 2 1

3 = 1 collision with player 3

2 = 1 collision with player 2

1 = 1 invalid

0 = 1 collision with player 0

Etc.

When looking for collisions with plotted objects, the bit number tells

what color register is assigned to the object the collision was with.

For example, to detect collisions between player 1 and plotted objects

(officially called the play field), P1PF [$D005 (53253)] is used.

P1PF, player 1 to ploted object collisions

7 6 5 4 3 2 1 0

-----------------

P1PF |unused | | | | |

-----------------

8 4 2 1

3 = 1 collision with COLOR3

2 = 1 " COLOR2

1 = 1 " COLOR1

0 = 1 " COLOR0

Etc.

Once a collision occurs it remains indicated in its collision

HITCLR [$D01E (53278)]. STA HITCLR or POKE 53278,0 will do.

Useful database variables and OS equates

HPOSP0 $D000 (53248): write: horizontal position of player 0

M0PF " " : read: missile 0 to plotted graphics collisions

HPOSP1 $D001 (53249): write: horizontal position of player 1

M1PF " " : read: missile 1 to plotted graphics collisions

HPOSP2 $D002 (53250): write: horizontal position of player 2

M2PF " " : read: missile 2 to plotted graphics collisions

HPOSP3 $D003 (53251): write: horizontal position of player 3

M3PF " " : read: missile 3 to plotted graphics collisions

HPOSM0 $D004 (53252): write: horizontal position of missile 0

P0PF " " : read: Player 0 to plotted graphics collisions

HPOSM1 $D005 (53253): write: horizontal position of missile 1

P1PF " " : read: Player 1 to plotted graphics collisions

HPOSM2 $D006 (53254): write: horizontal position of missile 2

P2PF " " : read: Player 2 to plotted graphics collisions

HPOSM3 $D007 (53255): write: horizontal position of missile 3

P3PF " " : read: Player 3 to plotted graphics collisions

SIZEP0 $D008 (53256): write: size of player 0

M0PL " " : read: missile 0 to player collisions

SIZEP1 $D009 (53257): write: size of player 1

M1PL " " : read: missile 1 to player collisions

SIZEP2 $D00A (53258): write: size of player 2

M2PL " " : read: missile 2 to player collisions

SIZEP3 $D00B (53259): write: size of player 3

M3PL " " : read: missile 3 to player collisions

SIZEM $D00C (53260): write: widths for all missiles

P0PL " " : read: player 0 to other player collisions

GRAFP0 $D00D (53261): write: player 0 graphics (used by OS)

P1PL " " : read: player 1 to other player collisions

GRAPF1 $D00E (53262): write: player 1 graphics

P2PL " " : read: player 2 to other player collisions

GRAFP2 $D00F (53263): write: player 2 graphics

P3PL " " : read: player 3 to other player collisions

GRAPF3 $D010 (53264): write: player 3 graphics

GRAFM $D011 (53265): write: missile graphics (used by OS)

COLPM0 $D012 (53266): color for player/missile 0

COLPM1 $D013 (53267): color for player/missile 1

COLPM2 $D014 (53268): color for player/missile 2

COLPM3 $D015 (53269): color for player/missile 3

COLPF0 $D016 (53270): color register 0

COLPF1 $D017 (53271): color register 1

COLPF2 $D018 (53272): color register 2

COLPF3 $D019 (53273): color register 3

COLBK $D01A (53274): background color (register 4)

PRIOR $D01B (53275): priority select, GTIA modes

GRACTL $D01D (53277): graphics control

HITCLR $D01E (53278): writing anything clears all collision bits

DMACTL $D400 (54272): direct memory access (DMA) control

PMBASE $D407 (54279): start of P/M memory

Shadow registers

SDMCTL $022F (559): DMACTL

GPRIOR $026F (623): PRIOR

PCOLR0 $02C0 (704): COLPM0

PCOLR1 $02C1 (705): COLPM1

PCOLR2 $02C2 (706): COLPM2

PCOLR3 $02C3 (707): COLPM3

COLOR0 $02C4 (708): COLPF0

COLOR1 $02C5 (709): COLPF1

COLOR2 $02C6 (710): COLPF2

COLOR3 $02C7 (711): COLPF3

COLOR4 $02C8 (712): COLBK

SOUND

Generating sound can be very simple. For simple sounds there are four

audio channels, each controlled by two control registers.

GENERATING SOUNDS

To generate a sound in channel 1, put the frequency and volume codes

into the frequency and control registers. The frequency register for

channel 1, AUDF1 [$D200 (53760)] can have any number from 0 to $FF

(255). 0 causes the highest frequency; 255 causes the lowest. The

volume/noise (control) register for channel 1, AUDC1 [$D201 (53761)]

is more complicated.

Audio channel control (volume/noise) register

7 6 5 4 3 2 1 0

-----------------

AUDCx | noise | volume|

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

The noise bits can have various values. The best way to learn to use

them is by experimentation. The technical details of the polynomial

counters which generate the noise has little bearing on what is heard.

The two special values of interest are: $1 (volume+16 in decimal),

which causes a DC voltage proportional to the volume bits and; $A

(volume+160), which causes a pure tone (square wave). The volume bits

select the relative volume, 0=off. Therefore, the number, $A8 (168

[8+160]) in AUDC1, will cause the frequency selected by AUDF1 to be a

pure tone of medium volume.

In BASIC the dirty work is done fore you. The SOUND command will do

all the calculations for you. The Sound command format is shown

below.

The BASIC sound command format

SOUND channel,frequency,noise,volume

The channel numbers is 0 to 3 instead of 1 to 4. The frequency, 0 to

255, is put into the frequency register. The noise is put into the

high bits of the channel control register with volume in the low bits.

Therefore...

SOUND 0,125,10,8

will produce a pure tone of medium frequency and volume in channel 0

(called channel 1 in assembly language).

ADVANCED SOUND

The Audio Control register, AUDCTL [$D208 (53768)], (not to be

confused with the four audio channel control registers), adds more

control for assembly language programmers. Again, to go into

technical details will be less productive than experimentation.

The audio control register. (AUDCTL)

7 6 5 4 3 2 1 0

-----------------

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

7 0 = 17 bit polynomial noise

1 = 9 bit below polynomial noise

6 0 = clock channel 1 with 64 KHz

1 = clock channel 1 with 1.79 MHz

5 0 = clock channel 3 with 64 KHz

1 = clock channel 3 with 1.79 MHz

4 0 = clock channel 2 with 64 KHz

1 = clock channel 2 with channel 1

3 0 = clock channel 4 with 64 KHz

1 = clock channel 4 with channel 3

2 1 = insert logical high-pass filter in

channel 1, clocked by channel 3

1 1 = insert logical high-pass filter in

channel 2, clocked by channel 4

0 0 = 64 KHz main clock

1 = 16 KHz main clock

All bits of AUDCTL are normally zero. The BASIC sound command causes

it to be reset to zero.

By clocking one channel with another, the range can be increased.

This essentially allows two channels with twice the range as each of

the four normal channels. This is called 16 bit sound.

To calculate exact frequencies, use the following formulas. The exact

clock frequencies are also given if more accuracy is needed. The

clock frequencies are acquired by dividing the signal from the TV

color-burst crystal. This crystal has a frequency of 3.579545 MHz.

Clock frequencies:

1.7897725 MHz (color-burst/2)

63.920446 Khz (color-burst/56)

15.699759 KHz (color-burst/228)

Formulas:

For 1.79 MHz

clock clock

f = ------------ f = ------------

2(AUDFn + 7) 2(AUDFn + 4)

16 bit 8 bit

AUDFn is the number in the audio frequency register.

For 16 KHz and 64 KHz

clock

f = ------------

2(AUDFn + 1)

AUDIO TIMER INTERRUPTS

When the audio timers count down to zero they generate IRQ interrupts

(if enabled). The timers can be reset by writing any number to STIMER

[D209 (53769)].

THE CONSOLE SPEAKER

The console speaker is where key clicks and the cassette signals come

from. On XL and XE models this speaker is heard through the TV

speaker. It is operated by toggling bit 3 of CONSOL [$D01F (53279).

This bit always reads 0 but it is actually set to 1 during vertical

blank.

Useful data base variables and OS equates

CONSOL $D01F (53279): bit 3 controls console speaker

AUDF1 $D200 (53760): Audio frequency 1

AUDC1 $D201 (53761): audio control 1

AUDF2 $D202 (53762): Audio frequency 2

AUDC2 $D203 (53763): audio control 2

AUDF3 $D204 (53764): Audio frequency 3

AUDC3 $D205 (53765): audio control 3

AUDF4 $D206 (53766): Audio frequency 4

AUDC4 $D207 (53767): audio control 4

AUDCTL $D208 (53768): general audio control

STIMER $D209 (53769): audio timer reset

THE JOYSTICK PORTS

The joystick ports are the I/O ports of the PIA chip. This means that

they are bidirectional, capable of output as well as input. The

joystick ports are usually set up for input. To read them, simply

read the port registers. PORTA [$D300 (53016)] will read joystick

ports 1 and 2. PORTB [$D301 (54017)] will read joystick ports 3 and

4. Joystick ports 3 and 4 are used for memory control on the XL/XE

models and don't have external connectors.

Each bit of each port can be configured independently for input or

output. To reconfigure a port, the port control registers, PACTL and

PBCTL [$D302 (54018) and $D303 (54019)], are used. The port control

registers also control some lines on the serial I/O connector.

The port control registers

7 6 5 4 3 2 1 0

PACTL -----------------

or |n 0 1 1 n n 0 n|

PBCTL -----------------

1 6 3 1 8 4 2 1

2 4 2 6

bits

PACTL

7 Peripheral A interrupt status. Set by peripheral

interrupt; reset by reading PORTA.

3 Cassette motor control (0 = on: 1 = off).

2 0 = PORTA is now port A direction control.

Writing to PORTA will now set bits for input

or output.

0 sets bit for input; 1 sets bit for output.

1 = PORTA operational

1 1 = peripheral A interrupt enabled.

PBCTL

7 Peripheral B interrupt status. Set by peripheral

interrupt; reset by reading PORTB.

3 Serial connector command line.

2 0 = PORTB is now port B direction control.

Writing to PORTB will now set bits for input

or output.

0 sets bit for input; 1 sets bit for output.

1 = PORTB operational

1 1 = peripheral B interrupt enabled.

The electronic configuration of the controller ports is as follows.

----------- -----------

\0 1 2 3 R/ \4 5 6 7 R/

\t + - L/ \t + - L/

------- -------

0 through 7 are the binary data bits for port A or port B.

+ and - are +5 volts and ground respectively.

R and L are the left and right game paddles.

t is the joystick trigger line.

The data bits in the joystick ports are used as follows for the

joysticks and game paddles.

The joysticks and the port registers

7 6 5 4 3 2 1 0

-----------------

PORTA |U|D|L|R|U|D|L|R|

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

paddle | | | |

triggers 3 2 1 0

PORTB -----------------

(400/800 |U|D|L|R|U|D|L|R|

only) -----------------

paddle | | | |

triggers 7 6 5 4

U = up

D = down

L = left

R = right

The joysticks may be read either directly from the port registers or

from the joystick shadow registers. During vertical blank, the data

in the port registers is separated and put into the shadow registers.

These registers are, STICK0 [$0278 (632)], STICK1 [$0279 (633)],

STICK2 [$027A (634)] and STICK3 [$027B (635)]. The triggers may be

read from the joystick trigger registers, TRIG0 - TRIG3 [$D010 - $D013

(53264 - 53267)]. These register have shadow registers, STRIG0 -

STRIG3 [$0284 - 0287 (644 -647)]. If these registers read zero the

associated triggers are pressed. The paddle triggers may be read from

their shadow registers also. They are, PTRIG0 - PTRIG 7, [$027C -

$0283 (236 - 643)].

THE GAME PADDLE REGISTERS

Although the game paddles are plugged into the joystick ports, they

are not read from the port registers. The game paddles are read by

first writing any number to the start-pot-scan register, POTGO [$D20B

(53771)]]. This turns off the capacitor dump transistors and allows

the pot reading

capacitors to begin charging. It also sets the TV scan line counter

to zero. As each capacitor crosses a certain trigger voltage, the

number of TV lines scanned is put in the respective pot value

transistors are turned on and the number 228 is put into any pot value

registers which are still empty.

Before reading the pot value registers, ALLPOT [$D208 (53768)] should

be checked. In this register, each bit corresponds to the validity of

a pot value register. If a bit is zero, its' associated pot value

go into the fast scan mode. In this mode the paddles are read in only

2 TV scan lines. They can also be read without regard to POTGO or

ALLPOT.

The pot value registers contain the number of TV scan lines it last

took for the paddle reading capacitors to charge (up to 228). These

registers are POT0 - POT7 [$D200 - $D207 (53760 -53767)]. Their

shadow registers are PADDL0 - PADDL7 [$0270 - $0277 (624 - 631)].

THE LIGHT PEN REGISTERS

Whenever a joystick trigger is pressed, the light pen registers, PENH

and PENV are updated. PENH [$D40C (54284)] takes a value based on a

color clock counter. The value can be from 0 to 227. PENV [$D40D

[54285)] takes the 8 highest bits of the vertical line counter. A

light pen is simply a photo transistor connected to a joystick trigger

line and focused on the TV screen. When the electron beam strikes the

part of the screen the light pen is focused on, the transistor turns

on pulling the trigger line low. The light pen registers then contain

numbers relative to where the light pen was pointing. The shadow

(566)).

Useful operating system equates

TRIG0 $D010 (53264): joystick triggers

TRIG3 $D013 (53268):

POT0 $D200 (53760): paddle value

POT7 $D207 (53767):

ALLPOT $D208 (53768): reads validity of pot values

POTGO $D20B (53771): starts paddle read

SKCTL $D20F (53775): bit 2 enables fast pot scan

PORTA $D300 (53016): port A data

PORTB $D301 (53017): port B data

PACTL $D302 (54018): port A control

PBCTL $D303 (54019): port B control

PENH $D40C (54284): light pen horizontal value

PENV $D40D (54285): light pen vertical value

Shadow registers

LPENH $0234 (564): light pen horizontal value

LPENV $0235 (566): light pen vertical value

PADDL0 $0270 (624): game paddle values

PADDL7 $0277 (631)

STICK0 $0278 (632): joystick registers

STICK0 $027B (635):

PRTIG0 $027C (636): paddle triggers

PTRIG7 $0283 (643):

STRIG0 $0284 (644): joystick triggers

STRIG3 $0287 (647):

MISC HARDWARE REGISTERS AND INFORMATION

VERTICAL LINE COUNTER

The ANTIC chip has a vertical line counter at $0D4B (54283). This

counter shows the high 8 bits of a 9 bit counter. This gives two line

resolution. The value of this counter is placed into PENV [$D40D

(54285)] when a joystick trigger is pressed.

SERIAL PORT REGISTERS

The POKEY chip has some registers which control the serial port.

The serial port control register, SKCTL [$D20F (53775)], controls the

serial port configuration and the game paddle scan mode. and some

keyboard circuitry.

The serial port control register

7 6 5 4 3 2 1 0

-----------------

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

bits

0 1 = enable keyboard debounce

1 1 = enable keyboard scan

both 0 = set initialization mode.

2 1 = fast pot scan

3 1 = serial output is two tone (for cassette)

instead of logical true/false

5 >- serial port mode control

7 1 = forced logical 0 on output

If the serial port control register is read from it gives the serial

port status. The register is then called SKSTAT

Serial port status register

7 6 5 4 3 2 1 0

-----------------

| | | | | | | |1|

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

bits

0 not used, reads 1

1 0 = serial input shift register busy

2 0 = last key is still pressed

3 0 = shift key pressed

4 0 = direct from serial input port

5 0 = keyboard over-run

6 0 = serial data input over-run

7 1 = serial data input frame error

The serial port status is latched and must be reset by writing any

number to its' reset register, SKRES [$D20A (53770)].

SERIAL PORT INPUT AND OUTPUT DATA

When a full byte of serial input data has been received, it is read

from the serial input data register, SERIN [$D20D (53773). Serial

output data is written to the same register, which is then called the

serial output data register, SEROUT. This register is usually written

to in response to a serial output data interrupt (bit 4 of IRQST).

HARDWARE CHIP MEMORY ALLOCATION

The addresses for the hardware chips are not completely decoded. For

example, the PIA needs only four bytes of memory but is active from

$D300 - D3FF. Enough room for 64 PIA chips. A second pair of

parallel ports could be added by accessing the address bus and further

decoding the address for a second PIA. (This would also require a

small modification of the computer's circuit board to disable the

original PIA when the new one is active.) Similarly, there is room

for 15 more POKEY or ANTIC chips and 7 gtia chips, should you ever

need them. (GTIA uses $D000 - D0FF, POKEY uses $D200 - $D2FF and

ANTIC uses $D400 - $D4FF.)

Useful data base variables and OS equates

SKRES $D20A (53770): serial port status reset

SEROUT $D20D (53773): serial output data

SERIN $D20D (53773): serial input data

SKCTL $D20F (53775): serial port control

SKSTAT $D20F (53775): serial port status

VCOUNT $D40B (54283): vertical line counter

Os shadow registers

SSKCTL $0232 (562): SKCTL

THE XL AND XE MODELS

BASIC B BUGS

Most of the Atari 600XL and 800XL models were supplied with the

"debugged" version B of Atari BASIC. This new BASIC got rid of the

minor bugs of BASIC A and introduced some new major bugs of it's own.

Each time a program is saved, 16 extra bytes are tagged onto the end

of the program. After many saves and reloads, as when developing a

long program, the program becomes too large for the memory.

The computer may lock up unpredictably.

Program line links may get messed up, leaving garbage in the listing

and the program unrunable.

Large LISTed programs may not run unless SAVed and reLOADed.

If the length of a listed program is a multiple of a certain number of

bytes, it will not run unless the length is somehow changed.

BASIC version B has been replaced by version C. All of the XE models

have this truly debugged version of BASIC.

NEW OPERATING SYSTEM PROBLEMS

I have heard of only one bug in the operating system in XL and XE

models. This is a mishandling of the printer timeout. The computer

cannot tell if there is a printer attached or not. This may have been

fixed in the XE models. However, many programs, some even formerly

sold by Atari, do not jump through published jump vectors when using

the operating system. These programs will not run on XL/XE models.

(Some of these programs are Atari Word Processor (not Atariwriter) and

LJKs Letter Perfect and Data Perfect.) Since the operating system ROM

can be switched to RAM, a "translator" can be used to load the 800

operating system into an XL or XE model.

130XE MEMORY MANAGEMENT

The 130XE has an extra 64K bank of memory. It is divided into four

blocks of 16K each. Each block can be switched to replace part of the

main bank of RAM from $4000 (16384) to $7FFF (32767). Furthermore, it

can be switched in such a way that only the 6502, or the ANTIC chip

can see the extra memory.

Port B (formerly the two extra joystick ports of the 400/800) is used

to manage the memory.

Port B and memory management

7 6 5 4 3 2 1 0

-----------------

PORTB |T|U|A|C|S S|B|R|

-----------------

1 6 3 1 8 4 2 1

2 4 2 6

R 1 = OS replaced by RAM

B 0 = BASIC enabled

S S bank select bits

C 0 = CPU sees switched RAM at $4000

A 0 = ANTIC sees switched RAM

U unused

T 0 = self test

Bits 2 and 3 of PORTB select which block of the extra bank of memory

is switched in.

Bank select bits

bits block

2 3 address

-------------------------

0 0 $0000 - $3FFF

0 1 $4000 - $7FFF

1 0 $8000 - $BFFF

1 1 $C000 - $FFFF

Bits 4 and 5 select which chip sees the switched in RAM at $4000 -

$7FFF

Chip select bits

bits ANTIC 6502

4 5

--------------------------

0 0 Ext. Ext.

0 1 Ext. Main

1 0 Main Ext.

1 1 Main Main

THE XL PARALLEL PORT

Pin out of the parallel port

top from rear

111112222233333444445

2468024680246802468024680

-------------------------

11111222223333344444

1357913579135791357913579

1 2 GND

3 A1 4 A0

5 A3 6 A2

7 A5 8 A4

9 GND 10 A6

11 A8 12 A7

13 A10 14 A9

15 A12 16 A11

17 A14 18 A13

19 A15 20 GND

21 D1 22 D0

23 D3 24 D2

25 D5 26 D4

27 D7 28 D6

29 GND 30 GND

31 GND 32 phase 2 clock

33 RESET 34

35 RDY 36 IRQ

37 37

39 40

41 GND 42

43 RAS 44

45 R/W 46 GND

47 +5V 48 +5V

49 GND 50

The phase 2 clock runs at 1.8 MHz. When the clock is high, the

address and R/W lines are valid. The clock goes from high to low,

when the data lines are also valid. All lines then become invalid.

The 130XE doesn't have the parallel port. However, it has a cartridge

slot expansion. This is a small cartridge-slot-like connector with

the necessary connector to use parallel expansion.

FINE SCROLLING

If address $026E (622) is $FF, graphics 0 will be in the fine scroll

mode.

OTHER ADDRESSES

DSCTLN [$0D25,2 (725)] is the disk sector size. should be $80 (128).

DMASAV [$02DD (735)] is a copy of the DMA control register, SDMCTL

[$022F (559)]. It is set up when a channel is opened to the screen.

The value is moved to SDMCTL whenever a key is pressed. It is used to

restore the display if DMA is disabled.

PUPBT [$033D,3 (829-831)] is used to test memory integrity when

[RESET] is pressed. If these bytes are not $5C, $93 and $25, the

computer will do a cold start when [RESET] is pressed.

The self-test ROM is from $D000 to $D7FF, the same addresses as the

hardware registers. This part of the operating system ROM is disabled

when not used. When The computer is put into the self-test mode, This

part of ROM is copied to $5000 to $57FF and run from there.

GINTLK [$03FA (1018)] is a logical 1 if a cartridge is installed

(built-in BASIC is considered a cartridge). BASIC can be disabled by

poking 1018 with a non-zero number. If [RESET] is then pressed, the

computer will attempt to load the DUP.SYS file and basic will be

completely disabled.

APPENDIX A

HARDWARE REGISTERS

Name Description Address Name Address

----------------------------------------------------------------------

ALLPOT game paddle ready indicators $D208 53768

AUDC1 Audio channel 1 control $D201 53761

AUDC2 Audio channel 2 control $D203 53763

AUDC3 Audio channel 3 control $D205 53765

AUDC4 Audio channel 1 control $D207 53767

AUDCTL general audio control $D208 53768

AUDF1 Audio frequency 1 control $D200 53760

AUDF2 Audio frequency 2 control $D202 53762

AUDF3 Audio frequency 3 control $D204 53764

AUDF4 Audio frequency 4 control $D206 53766

CHACTL character control $D401 54273 CHART $02F3 755

CHBASE Address of character set / 256 $D409 54281 CHBAS $O2F4 756

COLBK color/brightness of setcolor 4 $D01A 53274 COLOR4 $02C8 712

COLPF0 Color/brightness of setcolor 0 $D016 53270 COLOR0 $02C4 708

COLPF1 color/brightness of setcolor 1 $D017 53271 COLOR1 $02C5 709

COLPF2 color/brightness of setcolor 2 $DO18 53272 COLOR2 $02C6 710

COLPF3 color/brightness of setcolor 3 $DO19 53273 COLOR3 $02C7 711

COLPM0 color/brightness, player/missile 0 $D012 53266 PCOLR0 $02C0 704

COLPM1 color/brightness, player/missile 1 $DO13 53267 PCOLR1 $02C1 705

COLPM2 color/brightness, player/missile 2 $DO14 53268 PCOLR2 $02C2 706

COLPM3 color/brightness, player/missile 3 $DO15 53269 PCOLR3 $02C3 707

CONSOL [START], [SELECT], [OPT.], speaker $D01F 53279

DLISTH display list pointer high byte $D403 54275 SDLSTH $0231 561

DLISTL display list pointer low byte $D402 54274 SDLSTL $0230 560

DMACTL Direct Memory access control (DMA) $D400 54272 SDMCTL $022F 559

GRACTL graphics control $D01D 53277

GRAFM missile graphics $D011 53265

GRAFP0 player 0 graphics $D00D 53261

GRAFP1 player 1 graphics $D00E 53262

GRAFP2 player 2 graphics $D00F 53263

GRAFP3 player 3 graphics $D010 53264

HITCLR clear collisions $D01E 54278

HPOSM0 horizontal position of missile 0 $D004 53252

HPOSM1 horizontal position of missile 1 $D005 53253

HPOSM2 horizontal position of missile 2 $D006 53254

HOPSM3 horizontal position of missile 3 $D007 53255

HPOSP0 horizontal position of player 0 $D000 53248

HPOSP1 horizontal position of player 1 $D001 53249

HPOSP2 horizontal position of player 2 $D002 53250

HPOSP3 horizontal position of player 3 $D003 53251

HSCROL horizontal scroll $D404 54276

IRQEN interrupt request enable (IRQ) $D20E 53774 POKMSK $0010 16

IRQST IRQ status $D20E 53774

KBCODE keyboard code $D209 53769 CH $O2FC 764

M0PF missile 0 to graphics collisions $D000 53248

M0PL missile 0 to player collisions $D008 53256

M1PF missile 1 to graphics collisions $D001 53249

M1PL missile 1 to player collisions $D009 53257

M2PF missile 2 to graphics collisions $D002 53250

M2PL missile 2 to player collisions $D00A 53258

M3PF missile 3 to graphics collisions $D003 53251

M3PL missile 3 to player collisions $D00B 53259

NMIEN non-maskable interrupt enable (NMI)$D40E 54286

NMIRES NMI reset $D40F 54287

NMIST NMI status $D40F 54287

P0PF player 0 to graphics collisions $D004 53252

P0PL player 0 to player collisions $D00C 53260

P1PF player 1 to graphics collisions $D005 53253

P1PL player 1 to player collisions $D00D 53261

P2PF player 2 to graphics collisions $D006 53254

P2PL player 2 to player collisions $D00E 53262

P3PF player 3 to graphics collisions $DOO7 53255

P3PL player 3 to player collisions $D00F 53263

PACTL port A control $D302 54018

PAL Europe/North America TV indicator $D014 53268

PBCLT port B control $D303 54019

PENH light pen horizontal position $D40C 54284 LPENH $0234 564

PENV light pen vertical position $D40D 54285 LPENV $0235 565

PMBASE player/missile address / 256 $D407 54279

PORTA port A $D300 54016 STICK0 $0278 632

STICK1 $0279 634

PORTB port B $D301 54017 STICK2 $027A 634

STICK3 $027B 635

POT0 game paddle 0 $D200 53760 PADDL0 $0270 624

POT1 game paddle 1 $D201 53761 PADDL1 $0271 625

POT2 game paddle 2 $D202 53762 PADDL2 $0272 626

POT3 game paddle 3 $D203 53763 PADDL3 $0273 627

POT4 game paddle 4 $D204 53764 PADDL4 $0274 628

POT5 game paddle 5 $D205 53765 PADDL5 $0275 629

POT6 game paddle 6 $D206 53766 PADDL6 $0276 630

POT7 game paddle 7 $D207 53767 PADDL7 $0277 631

POTGO start pot scan sequence $D20B 53771

PRIOR p/m priority and GTIA mode $D21B 53275 GPRIOR $026F 623

RANDOM random number generator $D20A 53770

SERIN serial port input $D20D 53774

SEROUT serial port output $D20D 53773

SIZEM missile size $D00C 53260

SIZEP0 player 0 size $D008 53256

SIZEP1 player 1 size $D009 53257

SIZEP2 player 2 size $D00A 53258

SIZEP3 player 3 size $D00B 53259

SKCTL serial port control $D20F 53775 SSKCTL $0232 563

SKREST reset serial port status $D20A 53770

SKSTAT serial port status $D20F 53775

STIMER start timer $D209 53769

TRIG0 joystick trigger 0 $D010 53264 STRIG0 $0284 644

TRIG1 joystick trigger 1 $D011 53265 STRIG1 $0285 645

TRIG2 joystick trigger 2 $D012 53266 STRIG2 $0286 646

TRIG3 joystick trigger 3 $D013 53267 STRIG3 $0287 647

VCOUNT vertical line counter $D40B 54283

VDELAY vertical delay $D01C 54276

VSCROL vertical scroll $D405 54277

WSYNC wait for horizontal sync $D40A 54282

NUMERICAL ORDER

Registers sharing addresses are listed first when writen to, then when

read from

Name Description Address Name Address

----------------------------------------------------------------------

HPOSP0 horizontal position of player 0 $D000 53248

M0PF missile 0 to graphics collisions $D000 53248

HPOSP1 horizontal position of player 1 $D001 53249

M1PF missile 1 to graphics collisions $D001 53249

HPOSP2 horizontal position of player 2 $D002 53250

M2PF missile 2 to graphics collisions $D002 53250

HPOSP3 horizontal position of player 3 $D003 53251

M3PF missile 3 to graphics collisions $D003 53251

HPOSM0 horizontal position of missile 0 $D004 53252

P0PF player 0 to graphics collisions $D004 53252

HPOSM1 horizontal position of missile 1 $D005 53253

P1PF player 1 to graphics collisions $D005 53253

HPOSM2 horizontal position of missile 2 $D006 53254

P2PF player 2 to graphics collisions $D006 53254

HOPSM3 horizontal position of missile 3 $D007 53255

P3PF player 3 to graphics collisions $D007 53255

SIZEP0 player 0 size $D008 53256

M0PL missile 0 to player collisions $D008 53256

SIZEP1 player 1 size $D009 53257

M1PL missile 1 to player collisions $D009 53257

SIZEP2 player 2 size $D00A 53258

M2PL missile 2 to player collisions $D00A 53258

SIZEP3 player 3 size $D00B 53259

M3PL missile 3 to player collisions $D00B 53259

SIZEM missile size $D00C 53260

P0PL player 0 to player collisions $D00C 53260

GRAFP0 player 0 graphics $D00D 53261

P1PL player 1 to player collisions $D00D 53261

GRAFP1 player 1 graphics $D00E 53262

P2PL player 2 to player collisions $D00E 53262

GRAFP2 player 2 graphics $D00F 53263

P3PL player 3 to player collisions $D00F 53263

GRAFP3 player 3 graphics $D010 53264

TRIG0 joystick trigger 0 $D010 53264 STRIG0 $0284 644

GRAFM missile graphics $D011 53265

TRIG1 joystick trigger 1 $D011 53265 STRIG1 $0285 645

COLPM0 color/brightness, player/missile 0 $D012 53266 PCOLR0 $02C0 704

TRIG2 joystick trigger 2 $D012 53266 STRIG2 $0286 646

COLPM1 color/brightness, player/missile 1 $D013 53267 PCOLR1 $02C1 705

TRIG3 joystick trigger 3 $D013 53267 STRIG3 $0287 647

COLPM2 color/brightness, player/missile 2 $D014 53268 PCOLR2 $02C2 706

PAL Europe/North America TV indicator $D014 53268

COLPM3 color/brightness, player/missile 3 $D015 53269 PCOLR3 $02C3 707

COLPF0 Color/brightness of setcolor 0 $D016 53270 COLOR0 $02C4 708

COLPF1 color/brightness of setcolor 1 $D017 53271 COLOR1 $02C5 709

COLPF2 color/brightness of setcolor 2 $D018 53272 COLOR2 $02C6 710

COLPF3 color/brightness of setcolor 3 $D019 53273 COLOR3 $02C7 711

COLBK color/brightness of setcolor 4 $D01A 53274 COLOR4 $02C8 712

VDELAY vertical delay $D01C 54276

GRACTL graphics control $D01D 53277

HITCLR clear collisions $D01E 54278

CONSOL [START], [SELECT], [OPT.], speaker $D01F 53279

AUDF1 Audio frequency 1 control $D200 53760

POT0 game paddle 0 $D200 53760 PADDL0 $0270 624

AUDC1 Audio channel 1 control $D201 53761

POT1 game paddle 1 $D201 53761 PADDL1 $0271 625

AUDF2 Audio frequency 2 control $D202 53762

POT2 game paddle 2 $D202 53762 PADDL2 $0272 626

AUDC2 Audio channel 2 control $D203 53763

POT3 game paddle 3 $D203 53763 PADDL3 $0273 627

AUDF3 Audio frequency 3 control $D204 53764

POT4 game paddle 4 $D204 53764 PADDL4 $0274 628

AUDC3 Audio channel 3 control $D205 53765

POT5 game paddle 5 $D205 53765 PADDL5 $0275 629

AUDF4 Audio frequency 4 control $D206 53766

POT6 game paddle 6 $D206 53766 PADDL6 $0276 630

AUDC4 Audio channel 1 control $D207 53767

POT7 game paddle 7 $D207 53767 PADDL7 $0277 631

ALLPOT game paddle ready indicators $D208 53768

AUDCTL general audio control $D208 53768

KBCODE keyboard code $D209 53769 CH $O2FC 764

STIMER start timer $D209 53769

RANDOM random number generator $D20A 53770

SKREST reset serial port status $D20A 53770

POTGO start pot scan sequence $D20B 53771

SEROUT serial port output $D20D 53773

SERIN serial port input $D20D 53774

IRQEN interrupt request enable (IRQ) $D20E 53774 POKMSK $0010 16

IRQST IRQ status $D20E 53774

SKCTL serial port control $D20F 53775 SSKCTL $0232 563

SKSTAT serial port status $D20F 53775

PRIOR p/m priority and GTIA mode $D21B 53275 GPRIOR $026F 623

PORTA port A $D300 54016 STICK0 $0278 632

STICK1 $0279 633

PORTB port B $D301 54017 STICK2 $027A 634

STICK3 $027B 635

PACTL port A control $D302 54018

PBCTL port B control $D303 54019

DMACTL Direct Memory access control (DMA) $D400 54272 SDMCTL $022F 559

CHACTL character control $D401 54273 CHART $02F3 755

DLISTL display list pointer low byte $D402 54274 SDLSTL $0230 560

DLISTH display list pointer high byte $D403 54275 SDLSTH $0231 561

HSCROL horizontal scroll $D404 54276

VSCROL vertical scroll $D405 54277

PMBASE player/missile address / 256 $D407 54279

CHBASE Address of character set / 256 $D409 54281 CHBAS $O2F4 756

WSYNC wait for horizontal sync $D40A 54282

VCOUNT vertical line counter $D40B 54283

PENH light pen horizontal position $D40C 54284 LPENH $0234 564

PENV light pen vertical position $D40D 54285 LPENV $0235 565

NMIEN non-maskable interrupt enable (NMI)$D40E 54286

NMIRES NMI reset $D40F 54287

NMIST NMI status $D40F 54287

SHADOW REGISTER ORDER

ALPHEBETICAL ORDER