Re: PLL in PCI mode.

[Neal Palmer <neal@dinigroup.com>]

Anand,

  the issue is not whether or not a PLL can run slow enough.
The problem is that the original PCI specification allowed the clock
to be stopped at any time as long as the minimum period requirement
of 30ns was satisfied.  And a PLL (or DLL) can't track that.

  The 66Mhz PCI addendum required that the clock retain the same
period after reset has been deasserted (if the device is running
faster than 33Mhz).  PCI-X also requires that the clock not change
frequencies after the deassertion of reset.

  PCI-X effectively requires the use of a PLL because the maximum
clock to out is so small.  But 66Mhz PCI can be done without a PLL,
even in a .35um ASIC process.

-- Neal

On Sun, 28 Jul 2002, ANAND KURIAKOSE wrote:

> 	Hi Neal,
> 
> 	You said if the clock frequency is 33Mhz (Ofcourse PCI mode), then
> we are not allowed to use a PLL. Instead if the clock is 66Mhz (PCI or PCI-X
> mode), we can use a PLL. Let me clarify my boubt.
> 
> 	You made this statement because the PLL cannot handle low
> frequencies(33Mhz compared to 66Mhz) or is it because PCI-X mode doesnt
> support 33Mhz operation?
> 
> 	Regards,
> 	Anand.
> 
> 
> 
> 
> 	From:	Neal Palmer <neal@dinigroup.com> on 07/28/2002 09:51 PM
> 	To:	Kanti Ohri <kko@dcmtech.co.in>@SMTP@Exchange
> 	cc:	pci-sig@znyx.com@SMTP@Exchange 
> 
> 	Subject:	Re: PLL in PCI mode.
> 
> 
> 	Kanti,
> 
> 	  If you are running in 66Mhz PCI mode, then you are allowed to use
> a PLL.  
> 	But if you are running in 33Mhz PCI mode, then you are most
> definitely not 
> 	allowed to use a PLL (the clock can stop).
> 
> 	-- Neal
> 
> 	On Sun, 28 Jul 2002, Kanti Ohri wrote:
> 
> 	> Hello,
> 	> 
> 	> Is it Ok to use the PLL, in the PCI mode of operation, in PCI-X
> rev 1.0 to
> 	> meet the PCI timings?
> 	> 
> 	> Cheers,
> 	> KKO
> 	> 
> 
> 	-- 
> 	-- Neal Palmer
> 
> 	The Dini Group
> 	1010 Pearl St #6
> 	La Jolla, CA 92037
> 	(858) 454-3419 x16
> 	(858) 454-1728 (Fax)
> 
> 
> 

-- 
-- Neal Palmer

The Dini Group
1010 Pearl St #6
La Jolla, CA 92037
(858) 454-3419 x16
(858) 454-1728 (Fax)