American Megatrends MegaRAC M300V, User Manual

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Chapter Eight : Motherboard Hardware Support
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Chapter 8 Motherboard Hardware Support
Overview
This chapter provides more detail on the motherboard support required for OPMA compliance
along with sample implementation circuitry for OPMA-required signals. Refer to the appropriate
sections of this specification for detailed descriptions of the OPMA signals associated with these
support requirements and functions.
Note:
Some of these signals are not taken from the AMD OPMA Specification. Pay special attention to
the non-OPMA-required signals as they have been modified specifically for the MegaRAC
M300V card.
General Signal Termination
OPMA signal termination requirements for the motherboard are listed in
Chapter Four, OPMA
Interface Signal Specification
.
Fan Tachometer Read Back
The MegaRAC M300V card reads the fan tachometers through a 16:4 multiplexer located on the
motherboard. Only four fan tach signals are provided across the OPMA connector as inputs to the
MegaRAC M300V card. The 16:4 multiplexer is controlled by four MUX select signals provided
across the OPMA connector and the MegaRAC M300V card controls these signals to select one
bank of up to four fans to be monitored at a time. The motherboard must provide a 16:4
multiplexer for the MegaRAC M300V card to perform this function. The motherboard must also
provide appropriate pull-ups for the fan select signals. The following illustrations show the block
diagram and an example of the fan tach monitoring circuit, respectively.