Re: IEEE-1284 problem

On May 13, 6:19 am, Jon Elson <el...@xxxxxxxxxxxxxxxx> wrote:
Hello,

I have been making a motion control board that communicates
with a PC through the IEEE-1284 protocol of the PC parallel port
(EPP mode). It works fine using just any Dell desktop's
on-motherboard parallel port. I tried to use a SIIG regular-PCI
plug in card, and I get intermittent data garbling when data is
sent from my board to the PC. I have looked at the signals
extensively with both a scope and a logic analyzer, and can't
find any significant differences. Everything seems to matter,
ie. changing cable length, attaching logic analyzer, etc. alters
the frequency of the errors. I haven't been able to exactly
figure out what is going wrong, whether noise is causing
incorrect interpretation at my board's end or the PC end.
I'm guessing either my board is seeing noise on either ADDRSTB/
or DATASTB/ or nWRITE, or the PC end might be picking up noise
on nWAIT and sampling the data at the wrong time.

I have a fair amount of digital "filtering" of the signals in my
FPGA to exclude noise from the clock signals.

Has anyone used other IEEE-1284 PCI plug-in boards on custom
devices with good results? I specifically need something that
does the IEEE-1284/EPP modes flawlessly, as most of the later
motherboard chips seem to do. The SIIG card is a JJ-P00212-B,
which requires a DOS/Win 95 program to set the mode of the
parallel ports, which I did. (It apparently saves the setting
in a NV-ROM.)

Thanks in advance for any helpful thoughts!

Jon

Sounds like a transmission line issue to me;
poor ground eg using one ground wire instead of a ribbon with
ground wires in between each data line.
Signal reflections in the cable which will often cause
bit pattern dependant errors.

Have you looked at the IEE1284 spec for cables which,
if I remember correctly,
specifies things like the cable screen being connected
all the way round at the connectors, not a pigtail ?

Bob

.

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