On 3/17/08, Jinx wrote: > > > That's what Schmitt trigger inputs are for. > > Roman Black and I tested PIC GP i/o some years ago. We believed > it was possible to "fool" them with a very slowly changing voltage. > ISTR it was on the order of 0.1Hz, certainly way less than 1Hz I have really doubts. As long is about a good schmitd trigger you can't do that. Except maybe if you've coupled the input in AC with a large capacitor without any resistor on the input and varry the signal slighty below or above the schmitd trigger level. On the pin input that variation could not appear as long there is only a parasitical current charging path for the capacitor. The problem with slow signals is how long it takes (dV/dt) untill the signals pass the trigger thresold limit. All the passing time, the output is oscillating between low and high levels because the positive feedback is not enough for a stable change in the output. But the output of the trigger is changing from one level to another. > anyway. I'm a little hazy on the details but I think you could ramp > an i/p voltage from 0 to Vcc without causing a logic change inside > the chip > > There was more to it, some twist, but until I find the correspondence > between us (on a back-up CD) I can't say for sure what that was > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist