PCI Clock trace length between Bridges?

Hello

Im desiging a PCI Express card that have a PCI Express bridge (PCI Express one lane to PCI 66MHz) on the card edge connector.

The PCI Express bridge is connected to a PCI bridge (PCI to local bus) on my card.

PCI SPEC. determine the PCI clock trace lenght to be 2.5 inch for add-in card, but this is not the case in my card because the PCI bridge

is connected to a PCI Express bridge.

the question :

what is the pci clock trace length between the bridges and what is the pci data trace length between the bridges?

picture :

---------------------------------------------------------------------------= =AD---------

| | ---------------------------- | | PCI to local bus | | | | | ---------------------------- | pci clock trace /|\\ /|\\ data,control traces | | | | | | | --------------------------------- | | PCI express to PCI | | | | | ---------------------------------- | PCI Express x1 lane /|\\ | | | | | |

---------------------------------------------------------------------------= =AD---------

| | pci express connector ------------------

Reply to
raz_t
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I'm a hobbyist and have only scanned the PCI spec some years back, but I think there isn't a hard spec for what you are doing. (with add in boards, there are clear specs about the 2.5" serpentine CLK line and

10pF max loading, etc., but this sounds different to me.) So I think it gets back to the system timing budget you need to live within and you need to do the calcs. The length of the line and the signal velocity must meet the full round trip time allowed and the loaded impedance specs must be observed for every drive point, I think. I'm not clear about the express (haven't read about it and not even sure if that's the PCI X annex thing or not), but total round trip time at 33MHz is 10ns and at 66MHz is 5ns with a clock skew of 2ns and 1ns, respectively. But I'm sure you know that part of it.

I'm just suggesting the thought, only because you are asking after not getting an informed answer. I figure the worst I might do is get someone else correcting me about all this and learn a little by it.

Jon

Reply to
Jonathan Kirwan

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