Intel D15343-003 manual External Thermal Sensor Input, Usage

Intel® 82854 Graphics Memory Controller Hub (GMCH)

7.4External Thermal Sensor Input

An External Thermal sensor with a serial interface may be placed next to DDR SDRAM DIMM (or any other appropriate platform location), or a remote Thermal Diode may be placed next to the DDR DIMM (or any other appropriate platform location) and connected to the External Thermal sensor. Intel advises that the External Thermal sensor contains some form of hysteresis, since none is provided by the GMCH hardware.

The external sensor can be connected to the ICH4-M via the SMBus interface to allow programming and setup by BIOS software over the serial interface. The External sensor's output should include an Active-Low Open-Drain signal indicating an Over-Temp condition, which remains asserted for as long as the Over-Temp Condition exists, and deasserts when temperature has returned to within normal operating range. This External sensor output will be connected to the GMCH input (EXTTS_0) and will trigger a Preset Interrupt and/or Read-Throttle on a level- sensitive basis.

Additional External Thermal sensor's outputs, for multiple sensors, can be wire-OR'ed together allow signaling from multiple sensors located physically separately. Software can, if necessary, distinguish which DDR DIMM(s) is the source of the over-temp through the serial interface.

However, since the DDR DIMM(s) will be located on the same System Memory Bus Data lines, any GMCH-based Read Throttle will apply equally.

Note: The use of external sensors that include an internal pull-up resistor on the open-drain Thermal trip output is discouraged. However, it may be possible depending on the size of the pull-up and the voltage of the sensor. Please refer to the Intel® 854 Chipset Platform Design Guide For Use with Ultra Low Voltage Intel® Celeron® M Processor at 600 MHz (contact your Intel representative for the latest version of this document).

7.4.1Usage

External sensor(s) used for dynamic temperature feedback control:

•Sensor on DDR DIMMs, which can be used to dynamically control read throttling.

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