Some blind shots in the dark: Are your ISR variables accessed outside the ISR (i.e. in your main loop)? Have you declared them volatile? Are they 8 bit or 16? Handling rolling over correctly? On Wed, Dec 20, 2017 at 10:42 AM, andrew kelley wrote: > I further simplified it to a non USB, non interrupt main loop with blocki= ng > delay and outputting a incremented variable to latb and it still > glitches... Perhaps this chip is damaged. I'll swap it out with another a= nd > try again. Decoupling caps are on the power supply and the chip. > -- > http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > --=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 .