Laptop 595 support

[wjohn]

Phil

As always, you take the BS out of the discussion. Great post.

John.

[rjanuary]

Wow, thanks for all the advice! I will look into these suggestions and see what works for me and post it.

Is there a common problem forum, or FAQ setup where things like this can be posted for future reference? I'm sure this question will surface again if its a common occurance.

Richard

[P. Short]

This information should go into the wiki when it comes on-line.

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Phil

[Macrosill]

Phil,
Make a new thread titled FAQ and post the above. I will make it a sticky. Or I will do it with your permission.

[P. Short]

You have my permission...although you might wait to see if anyone else wants to add something or disagree with something that I said (give that parts of it are just my opinion).

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Phil

[Josh]

hit it on the nail Phil, i had to run a pullup with my 12 channel, probably have to do the same this year for my 595 or grinch, whichever i get done

[David V. Fansler]

Phil was elegant as usual with his summery of the situation, however my post just before his does point out that I did use an oscilloscope to observe the signals coming from the parallel port as I figured out what value pull up resistors to use. While not explicitly stated, I was also watching the output of the 74HC14 to see when the output signals were following the input from the parallel printer port.
David

[RJ]

If you use the newer chips on the grinch this wont be a problem. Phil is dead on in that with lower voltage and slower rise times there isn't enough voltage or sometimes enough time to get to the threshold of what the chip sees as a high signal. With the new chips instead of needing .8 * Vdd to register as a high you only need 2 volts. this takes less port voltage and less time to rise so it solves both problems. Can't help with the 595 chips as I never researched any direct replacements for them with lower thresholds I'm sure they exist. Either the allegro or the newer chip there testing will work for you grinch problems. RJ

[P. Short]

All of the Allegro parts that I have looked at (6276,6278,6279) seem to have a VIH of .7VDD (better than .8VDD, but not by much). The same is true of the one or two ST parts that I've looked at. Which parts are you referring to?

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Phil

[RJ]

The new chip that some of them were looking at that they posted the info on had a VIH of 2.0 volts I recommended they order a couple and try them but haven't heard anything more on it.