Re: Signal interference in a long cable

Hello!

Francesco Messineo wrote:

> what kind of termination did you use?

I tried a termination resistor. I used a potentiometer to try different
values from x Ohm to xxx Ohm, none had any visible impact.

> What gate drives the signal?

I believe it's a HMOS-II chip.

> Is the power to the driver and receiver chip very well bypassed?

I am not sure what that means :-(

> if it's really an "interference" (the exact term here is crosstalk)
> between two signals, you have to run a GND wire between each two data
> (or clock or whatever else) wires. That's how original parallel SCSI
> and HPIB bus cables were made. Of course these busses are also *very*
> well terminated.

That is a good idea, but it would mean I had to make my own cable
instead of using an off-the-shelf one. I can go there, but as a last resort.

> It might be a termination issue or a bypassing issue likely.
> You should first try to add a 47 ohm resistor just before the cable
> beginning at the driver side, on every signal (but VCC if any and
> GND).

Another good idea, but soldering resistors inside a C65 gives me chills
for some reason ;-) The receiver is also meant to work on a sock machine
without madifications.

> The take a picture of the scope with AC coupling, gnd clip on gnd pin
> of the driver and probe tip on the VCC pin of the driver. The do the
> same on receiver chip. This will show you if there's any ground or
> power bounce (bad decoupling in this case).

I will do that tomorrow, thanks.

> Also, whenever you suspect a crosstalk issue, take a picture of both
> signals, not just one :)

There are six signals in the cable, plus GND and reset. I am not sure
what crosstalks with what :-(

Regards,
Michau.



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