[SI-LIST] Re: 答复: about PCI clock length
- From: steve weir <weirsp@xxxxxxxxxx>
- To: myan@xxxxxxxxxxxxxx
- Date: Sun, 11 Apr 2004 06:06:12 -0700
Myan, I still think you are in trouble at 33MHz:
16 inches @ 150ps / inch 1 way = 4.8ns round trip propagation.
10ns = 2 round trips.
It is unlikely to work unless you do one of the following:
1) Push devices away from the middle of the bus.
2) Reduce the PCI clock speed.
3) Shorten the bus.
4) If you are lucky, and have very well behaved devices, add some selective
damping with series resistors in the bus.
The little bit of clock skew that you have is the least of your worries.
Steve
At 08:52 PM 4/11/2004 +0800, myan@xxxxxxxxxxxxxx wrote:
> Last email is wrong , This is correct.
>
> In our PCB :
> PCI device 1 | pci device 2 | mpc
> 8245 | pci device3 | pci device4
>|_____________|_____________|____________|____________|
> < -
> PCI bus - >
>
> The PCI host (mpc8245) is in the middle of the PCI bus
> The data sig trace length from PCI dev 1 to PCI dev
> 4 is 14 inch
> The clock sig trace length is 16 inch and it is
> equal to each device include MPC 8245
>
> Can it work ?
>
>
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Steve Weir
Teraspeed Consulting Group LLC
2926 SE Yamhill St.
Portland, OR 97214
(503) 239-5536
http://www.teraspeed.com
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