direction line weirdness
Can somebody help me debug this PicStep problem?
I am trying to drive a picstep board straight from my parallel port (breakout board is not done yet). I am able to get the step line to work but not the direction line. If I hard wire the the direction line to ground or +5 the stepper switches direction so I know the PIC and h-bridges are working. But if I try to change direction using the parallel port, no dice.
I have verified the parallel port works and is toggling between 100mV and 4.5V (referenced to the port ground) for both lines when disconnected from the picstep. Then I connect it to the PicStep and with the PicStep OFF (no power to the PIC or motor inputs that is), the step line continues to toggle the same full range but the direction line will only toggle the full range if the step line is high. If the step line is low, the direction line will only toggle between 80mV and 2.2V which won't switch directions of course. I have verified that the 10K pull-ups on direction and step are good.
I'm very much an electronics amateur so I may be missing something obvious but I would postulate that two lines driven the same way through identical circuitry would respond the same. Any guesses y'all?
Thank you very much.
It occurred to me as I reread this that since the PicStep board is not powered on, the pull-ups are of course doing nothing to pull up, duh. I still would expect both lines to act the same though. And the fact remains that when powered up the direction line does not work (can't remember what it measured when powered up but obviously low). The result being that I can step in one direction only when driven with CNC software.
Last edited by seware74; 02-27-2006 at 10:50 AM.
try adding a 7400 in a unity gain follower configuration or put abn optoisolator, like 4n25 between your printer port and step adn dir controller pins (increase fan-out and isolates the step and dir sinks/sources)
May also just want to try isolating step and dir pins with switching diodes.
-Just a thought
I too Saw this problem, it is to do t=with the motherboard working at 3v3 supply rail not 5V, to work around the problem either use a buffer gate or a transistor to swith logic levels, if you use a 74cmos gate wired as an "and" gate this should also work