IBM ThinkPad 770, Reference Manual

Page: 53 / 148

2. Reset the system microprocessor by writing a 1 to
bit 0.
3. Issue a Halt instruction to the system
microprocessor.
4. Reenable all maskable and nonmaskable interrupts.
If you do not follow this procedure, the results are
unpredictable.
Note: Whenever possible, use BIOS as an interface to
reset the system microprocessor to the real
mode. For more information about resetting the
system microprocessor, refer to the
IBM Personal
System/2 and Personal Computer BIOS
Interface.
System Control Port B (Hex 0061)
Bit definitions for the write and read functions of this port are shown
in the following figures:
Figure 2-31. System Control Port B (Hex 0061, Write)
Bit Function
7–4 Reserved
3 Enable channel check
2 Enable PCI SERR#
1 Enable speaker data
0 Timer 2 gate to speaker
Figure 2-32. System Control Port B (Hex 0061, Read)
Bit Function
7 PCI SERR# (PCI error) status
6 Channel check status
5 Timer 2 output
4 Toggles with each refresh request
3 Enable channel check
2 Enable PCI SERR# (PCI error) check
1 Enable speaker data
0 Timer 2 gate to speaker
Bit 7 If a system board error occurs and the PCI SERR# line is
activated, this bit is set to 1.
System Board 2-31