[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Microstrip line for PCI clock !!?



> I have seen a microstrip delay lines in serial to the PCI clock track
> in 3 of my PC add-on cards (nothing but a number of 360 degree bends
> on the track which effectively increase the track length). 
 
What you describe is called "serpentine" etch.

> Why this -- Any idea ?
 
As Peter Marek said, it's because that trace must be 2.5 inches long, in
order to meet the PCI Spec.  You will find it in section 4.4.3.1 of the
spec.

> Will it add to the performance ?
 
Well, not doing it will make the card NOT comply with the specification.

Every card must have it to control the clock skew.  If some cards use
0.5" and others use 4", they won't see the PCI CLK at the same time, and
this can cause timing violations, which could hang your computer.

Regards,
Andy