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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:
> You may need to have the flip-flop inside the PCIX I/O pad to get this
> Ganesan Viswanthan.
> American Megatrends Inc
> > ----------
> > From: Vikas M[SMTP:firstname.lastname@example.org]
> > Sent: Thursday, January 25, 2001 11:39 PM
> > To: email@example.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
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