Switch User Manual

Intel

82854 Graphics Memory Controller Hub (GMCH)

150 D15343-003

7.4 External 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).

7.4.1 Usage

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

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