Compaq MSB900L user manual System I/O map, Addr Function Size Comment

DIGITAL-LOGIC AG MSB900/L Detailed Technical Manual V1.0

5.9.2.System I/O map

The following table details the legacy I/O range for 000h through 4FFh. Each I/O location has a read/write (R/W) capability.

Note the following abbreviations:

---Unknown or can not be determined.

Yes	Read and write the register at the indicated location. No shadow required.
WO	Write only. Value written can not be read back. Reads do not contain any useful information.
RO	Read only. Writes have no effect.
Shw	The value written to the register can not be read back via the same I/O location. Read back is
	accomplished via a “Shadow” register located in MSR space.
Shw@	Reads of the location return a constant or meaningless value.
Shw$	Reads of the location return a status or some other meaningful information
Rec	Writes to the location are “recorded” and written to the LPC. Reads to the location return the re-
	corded value. The LPC is not read.

I/O Map

I/O Addr.	Function	Size	R/W	Comment
000h	Slave DMA Address - Channel 0	8bit	Yes	16bit values in two transfers.
001h	Slave DMA Counter - Channel 0	8bit	Yes	16bit values in two transfers.
002h	Slave DMA Address - Channel 1	8bit	Yes	16bit values in two transfers.
003h	Slave DMA Counter - Channel 1	8bit	Yes	16bit values in two transfers.
004h	Slave DMA Address - Channel 2	8bit	Yes	16bit values in two transfers.
005h	Slave DMA Counter - Channel 2	8bit	Yes	16bit values in two transfers.
006h	Slave DMA Address - Channel 3	8bit	Yes	16bit values in two transfers.
007h	Slave DMA Counter - Channel 3	8bit	Yes	16bit values in two transfers.
008h	Slave DMA Command/Status - Channels [3:0]	8bit	Shw$
009h	Slave DMA Request - Channels [3:0]	8bit	WO	Reads return value B2h.
00Ah	Slave DMA Mask - Channels [3:0]	8bit	Shw@	Reads return value B2h.
00Bh	Slave DMA Mode - Channels [3:0]	8bit	Shw@	Reads return value B2h.
00Ch	Slave DMA Clear Pointer - Channels [3:0]	8bit	WO	Reads return value B2h.
00Dh	Slave DMA Reset - Channels [3:0]	8bit	WO	Reads return value B2h.
00Eh	Slave DMA Reset Mask - Channels [3:0]	8bit	Shw@	Reads return value B2h.
00Fh	Slave DMA General Mask - Channels [3:0]	8bit	Shw@	Reads return value B2h.
010h-01Fh	No Specific Usage	---	---
020h	PIC Master - Command/Status	8bit	Shw$
021h	PIC Master - Command/Status	8bit	Shw$
022h-03Fh	No Specific Usage	---	---
040h	PIT – System Timer	8bit	Shw$
041h	PIT – Refresh Timer	8bit	Shw$
042h	PIT – Speaker Timer	8bit	Shw$
043h	PIT – Control	8bit	Shw$
044h-05Fh	No Specific Usage	---	---
Continued…

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