Re: PCI Clock Specs and PLL

["Yehuda D. Yizraeli" <yehuda@chipx.co.il>]

Ivor,

	Can you, please, broaden/expend on the following, 

	"If the clock and data/control buffers have the same prop delay, the 
timing is preserved." ... ... ... " you can adjust the tsu/th timing by using
buffers with different tpds for clock and data/control, at the expense of cycle 
time"

	Don't u miss the synchronization (second case) and what did u meant in 
the first case..?
	
	
	
					regards, yehuda
> 
> This subject was discussed quite a bit here a while back. You can check the
> archives for more information.
> 
> I think the conclusion was you can not use a PLL type chip for buffering the
> clock and still be compliant with the PCI spec. Some manufacturers modulate
> the clock to reduce EMI. 
> 
> You can use a fast buffer.
> 
> The IDT 74FCT807CT is a 1:10 clock driver with tpd of
> 1.3 nS (min) to 2.5 nS (max) into 50 ohm 10 pF load.
> 
> The Micro Linear ML65244 is a dual quad buffer/line driver with a
> tpd of 1.3nS (min) to 1.5nS (max) into a 500 ohm 50 pF lead.
> 
> If the clock and data/control buffers have the same prop delay, the timing
> is preserved. On the same note, you can adjust the tsu/th timing by using
> buffers with different tpds for clock and data/control, at the expense of
> cycle time.
> 
> At 10:24 AM 1/22/97 -0800, you wrote:
> >Hello PCI Community,
> >
> >PCI clock specs allow changing (and stopping) 
> >of PCI clock.  We are considering using the
> >PCI clock to drive our ASIC (for synchronization
> >benefits).  To control internal clock skew, we also 
> >want to include an on-chip PLL.
> >
> >But PLL won't work well with a reference clock
> >that could be changing.  Does anyone have any
> >good solutions for this problem?
> >
> >Or is it the case that people are ignoring this specs
> >and usually support only some fixed frequencies?
> >
> >Since our application is not in the portable environment,
> >is it safe to assume that stopping or changing the clock
> >is not very common?  Who are doing this today in
> >their systems?
> >
> >Thanks in advance for your help and feedback.
> >
> >- Ben -
> >
> >_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> >  Benson Cheung           (bcheung@adobe.com)
> >  Adobe Systems Inc.
> >  Printing & Systems Division
> >  M/S  P05
> >  303 Almaden Blvd.
> >  San Jose, CA  95110-2702
> >  (408) 536-2872            (408) 537-8411  (FAX)
> >_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
> >
> >
> >
> -Ivor
> 
> --------------------
> standard disclaimer:
> I speak for myself and my views may not be the same as my employer's.
> Ivor Bowden
> Peritek Corp
> phone: (510) 531-6500
> FAX: (510) 530-8563
> email: ivor@peritek.com
> 
> 


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