Dimm Sockets; Sdram Clock Buffer; Serial Eeprom; Lm75 Chip - HP P Class 450/500/550/600/650/700/750 Reference Manual

DIMM Sockets

Each DIMM socket is connected to the SMBus. The 168-pin DIMM modules used on the
HP V Personal Workstation include a 256 byte I2C Serial EEPROM. The first 128
ISUALIZE
bytes contain general information, including 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 Personal
Workstation.
The computer uses 8 KBytes of Serial EEPROM implemented within a single chip. 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.

LM75 Chip

The LM75 chip is a temperature sensor and alarm located on the system board. It is used
to measure the temperature in two areas of the Personal Workstation, and to send an
alarm to the processor in case of overheating.

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.
WARNING 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.

HP MaxiLife Utility

MaxiLife is a hardware monitoring chip which is resident on the system board. Its
responsibility includes On/Off and reset control, status panel management (Lock button,
Chapter 2
System Board
Devices on the SMBus
55