On 19 Dec 2017 at 8:57, andrew kelley wrote: > I'll check these suggestions out.. yes I am modifying the timer, but alwa= ys > the same value. I'll read again the section on it. (Err well until I chan= ge > it, which works). USB is event driven/polled in this application. I'll po= st > up what I find. You're probably on to this already, and we haven't seen your code, but stop= ping the=20 timer before writing to it will be important. Timer incrementing or decrementing in the midst of instructions accessing i= t messes=20 things up, with the kind of irregularities you're seeing. Especially a prob= lem with a=20 16 bit timer and 8 bit instruction width. --=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 .