NH82801HBM S LB9A Intel, NH82801HBM S LB9A Datasheet - Page 177

• Manufacturer Part Number: NH82801HBM S LB9A
• Description: CONTROLLER HUB, ICH8M, I/O, 82801HBM
• Manufacturer: Intel

Specifications of NH82801HBM S LB9A

• Power Dissipation Pd: 2.4W
• Digital Ic Case Style: BGA
• No. Of Pins: 676
• Pci Bus Type: I/O Controller Hub
• Pci Express Base Spec: PCIe 1.1
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional Description
5.13.10
5.13.10.1
Intel
®
ICH8 Family Datasheet
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 ICH8 implements an ALT access mode.
If the ALT access mode is entered and exited after reading the registers of the ICH8
timer (8254), the timer starts counting faster (13.5 ms). The following steps listed
below can cause problems:
After getting control in step #3, if the operating system does not reprogram the system
timer again, the timer ticks may be happening faster than expected. For example DOS
and its associated software assume that the system timer is running at 54.6 ms and as
a result the time-outs in the software may be happening faster than expected.
Operating systems (e.g., Microsoft Windows* 98, Windows* 2000, and Windows NT*)
reprogram the system timer and therefore do not encounter this problem.
For some other loss (e.g., Microsoft MS-DOS*) the BIOS should restore the timer back
to 54.6 ms before passing control to the operating system. 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.
Write Only Registers with Read Paths in ALT Access Mode
The registers described in
number field in the table indicates which register will be returned per access to that
port.
1. BIOS enters ALT access mode for reading the ICH8 timer related registers.
2. BIOS exits ALT access mode.
3. BIOS continues through the execution of other needed steps and passes control to
the operating system.
Table 73
have read paths in ALT access mode. The access
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