Devices On The Smbus; Piix4E Smbus Master Controller - HP P Class 450/500/550/600/650/700/750 Reference Manual

System Board

Devices on the SMBus

Devices on the SMBus
The SMBus is a subset of the I
maximum speed of 400 kHz. It is used to monitor some of the hardware functions of the
system board, (such as voltage levels, temperature, fan speed, DIMM presence and type)
both at system boot and during normal run-time. It is controlled by the SMBus controller
located in the PIIX4E chip.
Table 2-8. Devices on the SMBus
The following devices are connected to the SMBus:
• PIIX4E SMBus Master Controller 16 kHz maximum.
• DIMM sockets.
• SDRAM clock buffer.
• Serial EEPROM.
• Two LM75 temperature sensors.
• MaxiLife for hardware management, bus master controller 400 kHz maximum.
• LCD status panel.
An isolation mechanism is implemented, so that the LM 75 chips, MaxiLife monitoring
chip, and the Serial EEPROM can be accessed even when the computer is turned off. These
devices are powered through Vcc standby. A debug SMBus connector is also provided on
the system board for debug purposes. 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.
54
2
C bus. It is a two-wired serial bus which runs at a
Device
PIIX4E SMBus Master
Serial EEPROM
LM75
MaxiLife ASIC
SDRAM slot A1
SDRAM slot B1
SDRAM slot B2
PLL
SMBus Address
10
A8
90, 92
28
A0
A4
A6
D2
Chapter 2