Service manual

Troubleshooting 3-11
Monitor
The I
2
C bus monitors the state of system conditions scanned by the PCM. There are
two registers on the PCM:
• One records the state of the fans and power supplies and is latched when there is
a fault.
• The other causes an interrupt on the I
2
C bus when a CPU or system fan fails, an
overtemperature condition exists, or power supplied to the system is out of
tolerance.
The interrupt received by the I
2
C bus controller on PCI 0 alerts the system of
imminent power shutdown. The controller has 30 seconds to read the two registers
and store the information in the EEPROM on the PCM. The SRM console command
show power reads these registers.
Fault Display
The OCP display is written through the I
2
C bus.
Error State
Error state is written and read for power conditions. The state of the Halt button
(in/out) is read on the I
2
C bus.
Configuration Tracking
Each CPU, PCI bridge, PCI motherboard, and system motherboard has an EEPROM
that contains information about the module that can be written and read over the I
2
C
bus. All modules contain the following information:
• Module type
• Module serial number
• Hardware revision
• Firmware revision
• Memory size (only required for memory modules)