[SI-LIST] Re: PCI Timing Q?

  • From: Brahim Koudssi <brahim@xxxxxxxxxxxx>
  • To: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxx>
  • Date: Wed, 29 May 2002 08:36:22 -0700

Thank You Andrew And James,

 We are referring to the same clock, clk(i-1) and clk(i+1), I used clck(i-1) 
notation to signify the one that comes right after clk(i),
 my mistake, I am thinking of delayed clock cycle relative to clk(i) as being 

 I will use your notation in my next question:

 Tval (Max) and Tval (min)

 Is  Tval(max) measured relative to clk(i) and Tval(min) measured relative to 

Thanks again,

"Ingraham, Andrew" wrote:

> >  Tval is measured as the delay time between clk(i) and when the data is
> > valid, clk(i) precedes the data,
> >   Tval is measured at the driver output.
> >
> >   1.  Once the signals, clk and data arrive at the receiver, which clock
> > samples the data?
> >        Is it clk(i) or clk(i-1)?
> Neither.  It is clk(i+1), the one that comes next after clk(i).
> All PCI transfers go from one clock cycle to the next.  On the rising edge of 
> clock, outputs start to drive data after a delay of Tval.  Shortly (Tsu) 
> before the next rising edge of clock, the data that was sent is ready to be 
> received by an input.
> All this is happening all the time.  Data outputs are being driven on all 
> clock cycles, and received on all clock cycles, one clock cycle after being 
> sent.
> >   2.  The clock signal is from a board to the PCI expansion card, how's
> > the data sampled by  a board
> >         when the data is originating from the card?
> The clocks are timed to arrive at all devices on the bus at about the same 
> time, even those on PCI expansion cards.
> The data signals get from the expansion card to the motherboard through the 
> PCI connector.  The PCI connector makes an electrical connection for all 
> signals on the bus.  It is the same as if the device on the card was on the 
> motherboard, except that the "wires" to/from that device are longer (and 
> noisier).
> Andy

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