82801BA Datasheet, PDF (151/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

Functional Description
5.12.11 Alt Access Mode
Before entering a low power state, several registers from powered down parts may need to be
saved. In the majority of cases, this is not an issue, as registers have read and write paths. However,
several of the ISA compatible registers are either read only or write only. To get data out of write-
only registers and to restore data into read-only registers, the ICH2 implements an alternate access
mode.
5.12.11.1 Write Only Registers with Read Paths in Alternate Access Mode
The registers described in the following table have read paths in alternate access mode. The access
number field in the table indicates which register will be returned per access to that port.
Table 5-48. Write Only Registers with Read Paths in Alternate Access Mode
Restore Data
Restore Data
I/O
Addr
# of
Rds
Access
Data
I/O
Addr
# of
Rds
Access
Data
00h 2
1
DMA Chan 0 base
address low byte
2
DMA Chan 0 base
address high byte
1
Timer Counter 0 status, bits
[5:0]
2
Timer Counter 0 base count low
byte
01h 2
02h 2
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
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
03h 2
1
DMA Chan 1 base count
low byte
2
DMA Chan 1 base count
high byte
41h
1
7
Timer Counter 2 base count
high byte
Timer Counter 1 status, bits
[5:0]
04h 2
05h 2
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
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
06h 2
07h 2
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 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
82801BA ICH2 and 82801BAM ICH2-M Datasheet
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