PCI Noise

evaluation

They'd have to be very short. 8-)

Leon

Well, what's noise ;-) There's more to the PCI signaling environment than you may be aware of. I strongly suggest obtaining the PCI spec or if that isn't feasible this one may be of considerable (but not complete) help:

Cheers, Chris

generous coupling to ground with frequency matched capacitors will help you lengthen signal lines without noise degradation.

you

The lengths of the lines from the PCI bus connector are critical, and are quite short.

Leon

--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller

you

???

Please enlighten us.

Bob

I had a silimar problem in a different area (DDS's and A/D converters). The only solution was to throw away the ribbon and make a small pc board that interconnects the two eval boards, using a group plane beneth signal trance wires, and the approapriate connectors

I meant "ground plane" beneath the signal trace lines

beneth signal trance

as to the construction of the ribbon cable - you must solder your connections and wash the board of any flux and keep the length as short as practically possible.

Have I done it with PCI? no. Is is possible? probably. Does it meet IEE standards? of course not, but this is a one-off board.

good luck.

Hi,

If you study the PCI specs, you will see that there is a maximum lenght specified for the pcb traces (1.5" and 2.5 " for the clock line) . This is quite important because the signals and switching points rely on the reflected wave principle of the PCI bus.!!!

I suggest you obtain the PCI specs. Your io ports on your FPGA must also be pci compliant and you really should take care of the right timing constraints to and from the PCI io pads, otherwise you might experience a lot of problems on the PCI bus.

regards

ron proveniers

"Ted" schreef in bericht news:chf9eq$frj$ snipped-for-privacy@newsg2.svr.pol.co.uk...

evaluation

As a matter of clarity, the maximum length for most 32-bit PCI bus signals is 1.5" as you stated. But the clock line is specified to be 2.5" +-0.1" (2.4" to 2.6"). In other words, this is not a maximum length, it is a required length.

I agree that you must get the specification, as there are numerous other important details. Such as decoupling ALL supply lines even if you make no connection to them.

-- Greg snipped-for-privacy@hotmail.com.invalid (Remove the '.invalid' twice to send Email)

is

be

ribbon

If you read the PCI spec and apply a bit of thought, you'll realize the specs are on the conservative side. This is so that everyone and their dog can implement PCI cards that will work together in harmony and without issue.

Yes, the system is set to use reflected wave switching and the ideal wave will ring up on the first reflection; however, with a spec that says the line impedance can be anywhere between 60 and 100 ohms for PCI (compact PCI is much tighter), you will quickly realize there is going to be some ringy-dingies for a couple of round trips.

During development of PCI application card, it is common practice to use a PCI extender card. These typically extend the length of the PCI route going from the motherboard to the application card by 3-4 inches. The PCI signals typically look like crap, but they are settled by the time the clock arrives. These come in different varieties, some with ground planes, some without. I've used both with success when a few rules were followed (see below). Using a PCI extender card is similar to what you are trying to accomplish.

For the task at hand, i.e. connecting to a PCI card with ribbon, you would be best to limit your cable length to less than 4 inches. As a previous poster mentioned, you really really really really want these ribbons right above a ground plane (or grounded foil) that is tied on the PCI card and the FPGA card (as many points as you can). If your BIOS allows it, slow down your PCI bus clock, which will allow for longer settling time.

For best results, put the card in the PCI slot the furthest away from the motherboard chipset. Also, take out any (or all!) unneeded PCI cards from the backplane.

Good Luck

SM

is

be

ribbon

If you read the PCI spec and apply a bit of thought, you'll realize the specs are on the conservative side. This is so that everyone and their dog can implement PCI cards that will work together in harmony and without issue.

Yes, the system is set to use reflected wave switching and the ideal wave will ring up on the first reflection; however, with a spec that says the line impedance can be anywhere between 60 and 100 ohms for PCI (compact PCI is much tighter), you will quickly realize there is going to be some ringy-dingies for a couple of round trips.

During development of PCI application card, it is common practice to use a PCI extender card. These typically extend the length of the PCI route going from the motherboard to the application card by 3-4 inches. The PCI signals typically look like crap, but they are settled by the time the clock arrives. These come in different varieties, some with ground planes, some without. I've used both with success when a few rules were followed (see below). Using a PCI extender card is similar to what you are trying to accomplish.

For the task at hand, i.e. connecting to a PCI card with ribbon, you would be best to limit your cable length to less than 4 inches. As a previous poster mentioned, you really really really really want these ribbons right above a ground plane (or grounded foil) that is tied on the PCI card and the FPGA card (as many points as you can). If your BIOS allows it, slow down your PCI bus clock, which will allow for longer settling time.

For best results, put the card in the PCI slot the furthest away from the motherboard chipset. Also, take out any (or all!) unneeded PCI cards from the backplane.

Good Luck

SM

a

cables.