[SI-LIST] Re: Reflected Wave Switching - Silly Question.
- From: "Andrew Ingraham" <a.ingraham@xxxxxxxx>
- To: <si-list@xxxxxxxxxxxxx>
- Date: Thu, 2 Feb 2006 10:25:39 -0500
I'm not sure exactly what you are asking, but if your question boils down
to, "can anything other than PCI use reflected wave switching?" the answer
certainly is yes. Reflected wave switching has been around 'forever' ... a
lot longer than PCI has.
PCI is just a specification that happens to use CMOS technology. PCI
doesn't require CMOS, but that has been the prevailing technology for the
last several years. The PCI electrical specs (for 5V signaling) were
actually written to conform with the older TTL technology, even though most
mainstream digital electronics were already MOS, not bipolar by then.
I would be very cautious about using rules-of-thumb such as the maximum
trace delay is one or even two round-trips. There can be situations with a
lot of ringing that require more time to settle. Simulate!
A processor bus or RAM can be special cases designed to unique requirements,
and might behave differently than textbook reflected wave switching.
Regards,
Andy
> I am trying to understand basics of reflected wave routing.
> If I am making a PCB which has an onboard PCI bus then,
> I will be deciding topology & making calculations for number of loads C, L
> Tpd etc. and deciding the trace length = 2 round trip delay in a very
> general manner.
> this will be true considering PCI driver = capacitive Mos input stage,
> rise/fall time as per PCI specs. (4V/ns if I am not wrong).
>
> Leaving these 2 major parameters what is different in PCI driver....?
>
> Can I use the reflected wave routing strategy for any on board
> processor/ram bus or so which has cmos drivers with the same rise/fall
> time...?
>
> Will that work by doing all required calculations and simulations....?
>
> I apologies if I am wasting your time but this will help me understand
> basics more.
>
> Thanks & Regards,
> Kedar
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