Piix4E Smbus Master Controller; Dimm Sockets; Sdram Clock Buffer; Serial Eeprom - HP X Class 500/550MHz Reference Manual

System Board
Devices on the SMBus
An isolation mechanism is implemented, so that the LM75 temperature sensor, MaxiLife
monitoring chip, and the Serial EEPROM can be accessed even when the computer is
turned off. These devices are powered through Vcc standby. The PIIX4E and MaxiLife are
the two master devices.

PIIX4E SMBus Master Controller

The PIIX4E chip provides an intelligent processor-to-SMBus controller. All access is
handled by the processor through the PIIX4E SMBus interface. Typically, the processor
has access to all the devices connected to the SMBus.

DIMM Sockets

Each DIMM socket is connected to the SMBus. The 168-pin DIMM modules used on HP
V Personal Workstations include a 256 byte I2C Serial EEPROM. The first 128
ISUALIZE
bytes contain general information, including the DRAM chips' manufacturer, DIMM speed
rating, DIMM type, etc. The second 128 bytes of the Serial EEPROM can be used to store
data online. This will be used to store such information as ECC errors and possibly some
manufacturing related data (date module built or first installed, etc).

SDRAM Clock Buffer

The I2C 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 and also MaxiLife firmware.

Xeon Thermal Sensors

These sensors are located within the Single Edge Contact (SEC) cartridge. They are used
to measure temperature within the CPU, and this information is used to regulate the CPU
fan speed.
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