Atari ST Book: Internal Registers

By looking at the ROM code, available software and the hardware layout I can now document most specialty registers in the ST Book from Atari. I hope it is useful to you.

The main ROM for the ST Book starts at $e0000 and ends at $e3ffff (256kb large). At $e40000 starts the ROM-Disk (also 256kb large), which is automatically activated as drive P.

YM Port A

Bit Description
0 Side Select (S0SEL)
1 Disk 0 Select (D0SEL)
2 Disk 1 Select (D1SEL)
3 MAX241 Pin 20 (TI3) - RS232 RTS (/MFPRTS)
4 MAX241 Pin 6 (TI2) - RS232 DTR (/MFPDTR)
5 Centronics Strobe (STROBE)
6 IDE Reset (IDERESET)
7 FDD Dense Selection (FDD_DENSE_SEL)

Autovector Interrupt Level 7 /POWER FAIL (NMI)

MFP Input Pins

Bit Description
7 Power Alarms (Power Alarms) (POWER_ALARMS-) = (/SRCLOW
6 MAX241 Pin 22 (RD4) - RS232 CD (/MFPRI)
5 XDISKINT
4 KTDK (VBL) (KTOK)
3 XBLTINT
2 MAX241 Pin 26 (RD3) - RS232 CTS (/MFPCTS)
1 MAX241 Pin 5 (RD2) - RS232 DCD (/MFPCD)
0 Centronics Busy (BUSY)

$D0000 - Unknown $D0004 - Unknown

$FF820B

Bit Description
0 0: enable combo -> shadow controller video transfer, 1: disable combo -> shadow controller video transfer

$FF827E

Bit Description
0 0: Shadow Chip OFF
1 0: /SHIFTER_OFF output (Unused in STBook)
2 0: POWER_OFF (Turns off main VCC when high)
3 0: /22ON output (turns off LCD Bias when HIGH)
4 0: REFRESH_MACHINE output (turns on refresh controller)
5 0: RS-232_OFF output (turns off +/- 10 generator)
6 0: (Unused in STBook)
7 0: MTR_POWER_ON (turns on IDE drive motor supply)

$FF9200 (Configuration/Signal register)

Bit Description
0 0: Power Button pressed /(POWER_SWITCH)
1 0: Top is closed /(TOP_CLOSED)
2 0: RTC Alarm triggered /(RTC_ALARM)
3 0: “Common Source” voltage level below 7.2V /(SOURCE_DEAD) - triggers an NMI
4 0: “Common Source” voltage level below 8.8V /(SOURCE_LOW)
5 0: External Modem (Pin 10 on J204) /(MODEM_WAKE)
6 Reserved (always 1)
7 0: Triggered from the Expansion Port /(EXPANSION_WAKE)
8 Reserved
9 Reserved
10 Reserved
11 Reserved
12 Reserved
13 SELF TEST (?)
14 LOW SPEED FLOPPY
15 DMA AVAILABLE

$FF9210 8-bit Common Power Voltage Level in 100mV steps

$FF9214 8-bit Reference Voltage Level in 100mV steps

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