I further simplified it to a non USB, non interrupt main loop with blocking delay and outputting a incremented variable to latb and it still glitches... Perhaps this chip is damaged. I'll swap it out with another and try again. Decoupling caps are on the power supply and the chip. --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .