16f690 crashes

[Lincoln S.]

hey, my code is working great, but I have been running into some problems with noise. I geuss I should state the problem first. I am trying to get both input and output working on about a 1 foot long straight (four wires untwisted parrallel) serial cable to a PC. it worked ok before when I was just using on line and a ground, but now that I have input and output lines going to the pc, I get noise on the other line everytime I use the serout command from the pic. tried using 10k pulldowns (not being sure about the connection on that I ran 10k from data line to ground and the unused in from the pc as well). that didn't work. then I tried a 10 mf electrolytic on the unused line with neg side going to ground. this worked but it didn't quite seem kosher to be putting a 10mf electrolytic on a line of this sort, especially going to a PC serial line.

is there perhaps a post here with few help hints and some schematics showing how to reduce noise on straight cabling? I been looking for quite some time for some info to glean.

also worth noting, when I ran this pic (16f690).. just on the protoboard with intosc and nothing but power, I got no noise, so it is the parrallel capacitance of those wires doing it. recon I could try some cat5 I have lying around.. would be interested in all things noise reduction however.

I added an xtal btw. specs say +- 1 but in the area of millions of cycles per second, that could be a deal breaker.

thanks for any help. thanks for the help you allready gave me.

[mackrackit]

then I tried a 10 mf electrolytic on the unused line with neg side going to ground. this worked but it didn't quite seem kosher

Capacitors are the best way to reduce noise. I would guess the unused line is acting like an antenna and the cap is suppressing it.

[Lincoln S.]

huh.. I tried that electrolytic 10 mf cap. works fine across unused line from the pic. but I started wondering what it might do to the waveform of the incoming pc. I put it accross the pic out, and it went from high/low pulsing to low pulsing. anotherwords the cap is too high. I recon I'm going to have to pull out the old cap box I salvaged some years back and try some various values. I recon its about time to re-stock on the salvaged caps, the goo inside is prolly starting to dry up on the old ones. man.. I sure hope I don't have to find a scope to do this with, that would be a pain in the rear.

gotta hammer away some more and try to find some solutions. I think I am going to replace the wires with twisted pair cat 5 and see what that does.

[Acetronics2]

Hi, Lincoln

Why do you think ICs creators spend their efforts in creating LINE DRIVERS with as little as possible output impedance ???

Good question ... don't you think ?

Alain