RE: 25MHz PCI Interface

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

> For 33MHz PCI clock, 30.30ns clock period, 7ns setup time, 11ns Tval time;
 
Actually it can go up to 33.333..MHz or 30.000ns; picking nits.

> For 25MHz PCI clock, 40ns clock period, keeping Tval and Tprop unchanged,
> I can get extended setup time 16.70ns. Is it right?
 
Technically, Tval and Tsu stay the same, and Tprop is what can grow when the
clock period expands.  See the second paragraph in section 4.3.5 of the
spec.  Technically, only devices that go on motherboards can require a clock
speed slower than 33MHz.  See Note 1 below Table 4-5.

But for test purposes, where only you will ever use your chip, you could
bend the rules.

At 25MHz, Tcyc = 40ns and Tskew = 2ns.  Keeping Tval = 11ns and Tprop =
10ns, you could get away with Tsu = 17ns before timing breaks.

Regards,
Andy