Registers description

D301 PORTBS (WO)
Bits are mapped according to Atari mappings


D303 PBCTLS (WO)
Bit 2 - if set to zero, PORTB writes are disabled


D380 UCTL (WO)
Bits 1-0 - Memory expansion configuration mode
00 - Memory disabled
01 - 320k RAMBO
10 - 576k COMPY SHOP
11 - 1088K RAMBO
Bits 3-2 - System Select
00 - ROM Slot 1
01 - ROM Slot 2
10 - ROM Slot 3
11 - ROM Slot 4
Bit 4 - SDX disable, when set, SDX module is disabled
Bit 5 - reserved, should be written 0
Bit 6 - IO_RAM - enables (1) or disables (0) RAM in D600-D7FF address space. Used internally by BIOS code.
Bit 7 - CONFIG_L - configuration LOCK, when set, data in UCTL cannot be altered. At RESET this bit is set to 0 enabling BIOS code to alter configuration


D381 UAUX (WO)
Bit 0 - Controls pin M0 of P4 connector, BIOS default is SimpleStereo Enable/Disable
Bit 1 - Controls pin M1 of P4 connector, BIOS default is COVOX Enable/Disable
Bit 2 - Controls pin S0 of P4 connector
Bit 3 - Controls pin S1 of P4 connector
Bit 4 - when 0, WP Pin of P4 connector becomes D6xx signal for VBXE, when 1 D7xx
Bit 5 - when 0, VBXE decoder logic at pin WP is enabled, when 1 - Disabled


D381 UCOLDF (RW)
Bits 0-6 reserved, will read 0
Bit 7 - COLDF - 1 at power on, BIOS check this flag to see if Atari was just powered on, then writes 0.

All writes to Ultimate1MB registers are only possible when bit 7 of UCTL (CONFIG_L) is 0.

SDX Registers

D5E0 BANKNO (WO)
Bits 5-0 Bank number. Banks 0-53 are valid for SDX module. Bank 54 is BASIC ROM, bank 55 is MISSLE COMMAND or any other 8k game ROM image, banks 56-63 are for OS ROM slots. Access to all banks is provided through this port for flashing purposes
Bit 6 External Cartridge. When set, and Bit 1 is set, external cartridge is OFF, SDX is OFF
When reset, and bit 7 is set, external cardridge is ON, SDX is OFF
Bit 7 SDX Enable. When set, SDX is ON, External cartridge is always OFF


D3E2 RTCOUT (W)
Bit 0 Chip Enable
Bit 1 SPI Clock
Bit 2 SPI MOSI (Master Out, Slave In)
Bits 7-3 Reserved


D3E2 RTCIN (R)
Bit 0-2 Reserved
Bit 3 SPI MISO (Master In, Slave Out)
Bit 7-4 Reserved

Ultimate1MB FLASH Chip Memory Map

0x000000-0x04FFFF SDX
0x050000-0x053FFF BIOS code space
0x054000-0x05FFFF reserved
0x060000-0x061FFF BASIC
0x062000-0x063FFF 8k GAME cartridge
0x064000-0x06FFFF reserved
0x070000-0x073FFF 1st OS slot
0x074000-0x077FFF 2nd OS slot
0x078000-0x07BFFF 3rd OS slot
0x07C000-0x07FFFF 4th OS slot