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RE: PCI-X I/O pads




Worse yet.  You probably need to have a tightly controlled connection
between the IO PAD and the FF (i.e. make the FF part of the IO cell), and
you will definitely need to have a PLL.  That's one of the un-written
realities of a PCIX design.

On Fri, 26 Jan 2001, Ganesan Viswanathan wrote:

> Hi,
> 
> You may need to have the flip-flop inside the PCIX I/O pad to get this
> timing.
> 
> Ganesan Viswanthan.
> American Megatrends Inc
> 
> > ----------
> > From: 	Vikas M[SMTP:vikas_mj@yahoo.com]
> > Sent: 	Thursday, January 25, 2001 11:39 PM
> > To: 	pci-sig@znyx.com
> > Subject: 	PCI-X I/O pads
> > 
> > Hi,
> >  
> > I am currently involved in developing a PCI-X chip. The problem I am
> > facing
> > is meeting the Output Valid time of 3.8ns as specified by the PCI-X
> > specification. The signal from the core logic is registered and it passes
> > through two buffers and then the PCI-X I/O pad. The delay in this path is
> > clock-to-Q of flop ( 0.6),Buffer delay (0.6ns), the PCI-X I/O pad delay (
> > 2.3ns ) 
> > and a clock insertion delay (0.5ns ). With this amount of delay it is not
> > possible 
> > to meet the output valid time of 3.8ns.
> > 
> > I would appreciate if somebody can provide some idea on how this timing of
> > 3.8ns can be achieved if the PCI-X I/O pad delay itself is around 2.5ns ?
> > Are you aware 
> > of any technology library that has PCI-X  I/O pads with less than 2.0ns
> > output delay so that 
> > this timing can be achieved ?
> > 
> > Thanks in advance for your help,
> > Vikas M
> > 
> >  
> > 
> 

-- Neal Palmer

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