82801DB Datasheet, PDF (149/587 Pages) Intel Corporation – Intel 82801DB I/O Controller Hub 4 (ICH4)

Functional Description
For other operating systems (e.g., MS-DOS) the BIOS should restore the timer back to 54.6 ms
before passing control to the OS. If the BIOS is entering ALT access mode before entering the
suspend state it is not necessary to restore the timer contents after the exit from ALT access mode.
5.12.9.1 Write Only Registers with Read Paths in ALT Access Mode
The registers described in Table 5-46 have read paths in ALT access mode. The access number
field in the table indicates which register will be returned per access to that port.
Table 5-46. Write Only Registers with Read Paths in ALT Access Mode (Sheet 1 of 2)
Restore Data
Restore Data
I/O
Addr
# of
Rds
Access
Data
I/O
Addr
# of
Rds
Access
Data
00h 2
01h 2
02h 2
03h 2
1 DMA Chan 0 base address low byte
2
DMA Chan 0 base address high
byte
1 DMA Chan 0 base count low byte
2 DMA Chan 0 base count high byte 40h 7
1 DMA Chan 1 base address low byte
2
DMA Chan 1 base address high
byte
1 DMA Chan 1 base count low byte
2 DMA Chan 1 base count high byte 41h 1
1 Timer Counter 0 status, bits [5:0]
2 Timer Counter 0 base count low byte
3 Timer Counter 0 base count high byte
4 Timer Counter 1 base count low byte
5 Timer Counter 1 base count high byte
6 Timer Counter 2 base count low byte
7 Timer Counter 2 base count high byte
Timer Counter 1 status, bits [5:0]
04h 2
05h 2
06h 2
07h 2
08h 6
1 DMA Chan 2 base address low byte 42h 1
2
DMA Chan 2 base address high
byte
70h 1
1 DMA Chan 2 base count low byte
C4h 2
2 DMA Chan 2 base count high byte
1 DMA Chan 3 base address low byte
2
DMA Chan 3 base address high
byte
C6h 2
1 DMA Chan 3 base count low byte
C8h 2
2 DMA Chan 3 base count high byte
1
DMA Chan 0–3 Command²
2 DMA Chan 0–3 Request
CAh 2
3 DMA Chan 0 Mode: Bits(1:0) = “00”
CCh 2
4 DMA Chan 1 Mode: Bits(1:0) = “01”
5 DMA Chan 2 Mode: Bits(1:0) = “10”
CEh 2
6 DMA Chan 3 Mode: Bits(1:0) = “11”.
Timer Counter 2 status, bits [5:0]
Bit 7 = NMI Enable,
Bits [6:0] = RTC Address
1 DMA Chan 5 base address low byte
2 DMA Chan 5 base address high byte
1 DMA Chan 5 base count low byte
2 DMA Chan 5 base count high byte
1 DMA Chan 6 base address low byte
2 DMA Chan 6 base address high byte
1 DMA Chan 6 base count low byte
2 DMA Chan 6 base count high byte
1 DMA Chan 7 base address low byte
2 DMA Chan 7 base address high byte
1 DMA Chan 7 base count low byte
2 DMA Chan 7 base count high byte
Intel^® 82801DB ICH4 Datasheet
149