On Thu, 29 Apr 1999 08:26:52 -0500 "robert a. moeser" writes: >so... it seems that the two processors can affect each the other's >clock. and i had an explanation for the capacitor.., without it, the >two >PICs could "synchronize" due to power supply coupling. That's entirely possible, though of course you can't depend on it happening. The protocol you describe should have a large tolerance for clock speed mismatch. Perhaps there is a bug in the implementation, it so it actually needs the speeds to match. Try testing on F84's with deliberately different crystals. Using 4.00 MHz and 3.58 MHz should be a good approximation of the worst case difference between two 12C509's. Programs can also fail on JW parts because light coming in the window causes them to operate differently. If the light is weak, it will probably only cause the RAM locations to be different at power-on. Unless your software is defective, that shouldn't matter. Strong light can cause the PIC to malfunction. Cover the window during tests. Also JW parts will give uncertain results if they haven't been fully erased. Bits in the program memory that should have been erased to 1 will revert back to 0, especially at low voltage. ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866]