59
2 System Board
The Input/Output Controller Hub (82801AA)
DIMM Sockets
Each DIMM socket is connected to the SMBus. The 168-pin DIMM modules
include a 256 byte I
2
C Serial EEPROM. The first 128 bytes contain general
information, including the DRAM chips’ manufacturer’s name, DIMM speed
rating, DIMM type, etc. The second 128 bytes of the Serial EEPROM can be
used to store data online.
RIMM Sockets
Each RIMM socket is connected to the SMBus. The 168-pin RIMM modules
include a 256 byte I
2
C Serial EEPROM. The first 128 bytes contain general
information, including the DRAM chips’ manufacturer’s name, RIMM speed
rating, RIMM type, etc. The second 128 bytes of the Serial EEPROM can be
used to store data online.
Hardware Monitoring
ASIC
The Hardware Monitoring ASIC chip is a sensor dedicated to the processor
temperature. This chip uses the thermal diodes integrated into each
processor cartridge and makes the temperature information available
through the SMBus.
SDRAM Clock Buffer
The I
2
C port of the SDRAM clock buffer is connected to the SMBus. It can
be used to stop the unused clocks.
Serial EEPROM
This is the non-volatile memory which holds the default values for the CMOS
memory (in the event of battery failure).When installing a new system
board, the Serial EEPROM will have a blank serial number field. This will be
detected automatically by the BIOS, which will then prompt the user for the
serial number which is printed on the identification label on the back of the
PC Workstation. The computer uses 16KBytes of Serial EEPROM
implemented within two chips. Serial EEPROM is ROM in which one byte at
a time can be returned to its unprogrammed state by the application of
appropriate electrical signals. In effect, it can be made to behave like very
slow, non-volatile RAM. It is used for storing the tatoo string, the serial
number, and the parameter settings for the
Setup
program as well as
MaxiLife firmware.
Main PLL
The registers of the main PLL are accessed through the SMBus. These
registers control the PLL clock signal outputs and are write-only.Writing
over the SMBus may be destructive to the PC Workstation as it allows access
to information necessary to the System BIOS, without which the system will
not run.
