Re[n]: Wanted...PCI bus 3V driver/receiver models

Andy Ingraham ([email protected])
Thu, 29 Feb 96 10:22:08 EST

Scott McMorrow wrote:

> In a 5 volt signaling environment with 3.3V voltage level devices, you may want
> to be careful about low to high switching of the 3.3 V devices on the bus. 5
> volt devices will overshoot far enough to turn on the high clamp diodes,
> supressing the ringback component to reasonable levels. But with 3.3 volt
> drivers, all of the overshoot energy will ringback and can enter the threshold
> region of receivers on the PCI bus. With small geometry, fast devices, there
> can be an extreme amount of overshoot.

This is indeed a very good point. It's quite true. You can get some
rather long bus delays (settling times) which exceed the 10ns PCI spec.

I'm glad others out there are recognizing this problem.