Re: IEEE-1284 problem

Jon Elson wrote:
Tim Wescott wrote:

Are you terminating the signals properly? Is your add-in board terminating the signals properly?
Well, you work with the same things too long, and you get to thinking you know an awful lot about it! Terminating the data lines was the problem. Probably a case of too many lines changing state at the same time, causing crosstalk on the strobe lines. Anyway, the magic recipe appeared when I terminated only THREE of the 8 data lines to 3.3 V with 390 Ohm resistors. Suddenly it was running several hundred thousand cycles of the diagnostic with no errors.

Of course, I thought that wasn't going to do any good, because it didn't do any good on a different par port card and a different type of peripheral board in the past, with somewhat different timing. I'm guessing the receivers on this PC par port card have different thresholds, making them more sensitive to the noise. (Of course, I will actually terminate all 8 data lines, and if terminating the incoming control strobes is not counterproductive, I'll terminate them, too.)

Well, thanks MUCH for the kick in the pants needed to try some conventional bus integrity measures over again with a fresh view. I'll have to patch the new boards that haven't even arrived from the fabricator yet before I can re-spin the layout.
Thanks goodness I only ordered 25 boards!

Jon

That's why engineers are bald in front -- it's from slapping ourselves in the forehead and rubbing off all the hair.

I was thinking about your comment that you have to get it working with what's out there, not just to the spec -- but I didn't want to make you bear another cross unless you already had to.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html
.

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