HP XA LM75 Chip, Main PLL, WARNING:

2 System Board

Devices on the SM Bus

LM75 Chip

The LM75 chip is a temperature sensor and alarm located on the system board. It is used to measure the temperature in one area of the PC Workstation, and to send an alarm to the processor in case of overheating. This chip includes a security mechanism which prevents the system fan from being disabled using software controls so long as the temperature measured by the sensor is above the maximum operating temperature.

Main PLL

The registers of the main PLL are accessed through the SM bus. These registers control the PLL clock signal outputs and are write-only.

WARNING:Writing over the SM bus may be destructive to the PC Workstation, as it allows to access information necessary to the System BIOS, without which the system will not run.

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