>> O.K. So no one is using a 16C73A's A-D? Yep - use it all the time (except I now use the '73B). I DEFINITELY get readings from 00 thru FE or FF - I have not looked at the code for that project for quite some time - we ship several systems each month and I have not had to revisit that part of it for a couple of years now. The fact that you get higher readings when you put a low pass filter on the a/d input suggests to me that you have a noise problem either with the reference or the input. I use VDD as my reference - each input prior to the MUX has an input filter of 1uF / 10K. The MUXes feed RA0 and RA1 (I mux 8, 16, or 32 inputs each into RA0, RA1 for a total of up to 64 inputs). This is also a decent amount of bypassing right at the '73's GND and VDD pins. Quick thought - do you have BOTH ground pins connected toghether with a real short wire or trace? Not sure what else I can add. I have always found the a/d section to be reliable in the 16c71, 16c73A&B, 16c74A, 12c671. Don't know about the others . dwayne Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 15 years of Engineering Innovation (1984 - 1999) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. My posting messages to Usenet neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email.