On Wed, 29 Jul 2009 17:56:53 +0100 "Steve Smith" wrote: > During a program I have to periodically make a burst of 455Khz pulses > and stop when a pin changes state.... You won't be able to generate 455 exactly, so give that up, and generate 1/3 of that (or even 1/5). Then couple the output to a 455 kHz IF transformer to filter it. As the harmonics are odd, energy will be only 1/3, but you'll have more time to dedicate to generating the exact frequency. John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist