From: Brent Brown > > I have 390k and 82pF on a PIC16F84A which runs nicely > at 25kHz with a 5V supply Fits with the graph 220k + 100p = 35kHz 470k + 100p = 17kHz 390k +100p would be around 20kHz, 390k + 82p 24kHz The RC circuit is not the most stable part of the PIC but it should be repeatable. It varies with temperature and, even with a trimmer, it wouldn't pay to use the PIC under those circumstances for any long-string comms that require precise timing. It should be OK for apps where periodic synching can be done though -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics