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Re: 66MHz or 33MHz PCI Bus




>>>>> "Ingraham," == Ingraham, Andrew <Andrew.Ingraham@compaq.com> writes:
    >> How does PCI devices sitting on a PCI bus knows what are the speed of

  it can't.

    >> the PCI bus that it is sitting on, since the M66ENA pin is not a
    >> required pin for PCI devices. Thanks.
 
    Ingraham,> Simple.  If pin M66EN (pin 49B) is low, then it is a 33MHz
    Ingraham,> bus, or a 66MHz bus running at or below 33MHz.  If M66EN is
    Ingraham,> high, then it is a 66MHz bus with only 66MHz cards present,
    Ingraham,> running in the 33-66MHz range.

  If M66EN is high, then the system may run the bus at up to 66Mhz.
  If M66EN is low, then the system may only run the bus up to 33Mhz.

  The system in both cases may run the bus at any speed it wants. It can
run a system that says it is capable of 66Mhz, and run it at 12Mhz if it
wants to.

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