832-847



You can easily POKE the necessary values into the memory locations
and use a machine language subroutine through a USR function to call
the CIO directly (you must still use an OPEN and CLOSE statement for
the channel, however). This is useful because BASIC only supports
either record or single byte data transfer, while the CIO will handle
complete buffer I/O. See the CIO entry address, location 58454
($E456), for more details. These blocks are used the same way as the
page zero IOCB (locations 32 to 47; $20 to $2F). The OS takes the
information here, moves it to the ZIOCB for use by the ROM CIO, then
returns the updated information back to the user area when the
operation is done.
Note that when BASIC encounters a DOS command, it CLOSEs all
channels except zero. Refer to the Atari Hardware Manual and the 850
Interface Manual for more detailed use of these locations.

832-847        340-34F        IOCB0
     I/O Control Block (IOCB) zero. Normally used for the screen
     editor (E:). You can POKE 838,166 and POKE 839,238 and send
     everything to the printer instead of to the screen (POKE 838,163,
     and POKE 839,246 to send everything back to the screen again).
     You could use this in a program to toggle back and forth between
     screen and printed copy when prompted by user input. This will
     save you multiple PRINT and LPRINT coding.

     You can use these locations to transfer data to other devices as
     well since they point to the address of the device's "put one byte"
     routine. See the OS Manual for more information. Location 842
     can be given the value 13 for read from screen and 12 for write to
     screen. POKE 842,13 puts the Atari into "RETURN key mode" by
     setting the auxiliary byte one (ICAX1) to screen input and
     output. POKEing 842 with 12 returns it to keyboard input and
     screen output mode. The former mode allows for dynamic use of
     the screen to act upon commands the cursor is made to move
     across.

     You can use this "forced read" mode to read data on the screen
     into BASIC without user intervention. For example, in the
     program below, lines 100 through 200 will be deleted by the
     program itself as it runs.

     10 GRAPHICS 0:POSITlON 2,4
     20 PRINT 100:PRINT 150:PRINT 200
     25 PRINT "CONT"
     30 POSITION 2,0
     50 POKE 842,13:STOP
     60 POKE 842,12
     70 REM THE NEXT LINES WILL BE DELETED
     100 PRINT "DELETING..."