RE: Real PCI Clock Rates

["Ingraham, Andrew" <Andrew.Ingraham@compaq.com>]

>also note that "33MHz" systems can have the clock change
>dynamically, even stop. My PC bios has an option to
>enable/disable "spread specturm" PCI clocking. This means
>you can't use PLL type ("0 nS delay") clock chips to
>receive the clock. "66MHz" systems have to have a fixed
>frequency, so this isn't a problem.

66MHz systems CAN have a "spread spectrum" clock.  There are restrictions in
the (Rev. 2.2) Spec about how quickly that clock can vary, so downstream
PLLs should be designed to track it.

(By the way, there is a typo in Table 7-3 of the Rev. 2.2 Spec.  Fspread,
the last item, should range from -1% to 0% ... not 9%.)

Regards,
Andy