Steve:

Here are the conifgs:
@ device pic16F873A, HS_OSC ' High Speed Crystal/Resonator, 4 MHz and above
@ device pic16F873A, WDT_ON ' Watchdog timer enabled
@ device pic16F873A, PWRT_ON ' Power on timer enabled
@ device pic16F873A, BOD_ON ' Brown out detect enabled

There is a 0.1uf between Vss and Vdd

The Vdd has less than 1mV of ripple.

Both Vss pins are tied to ground.

I added the following to my configs, still no change.
@ device pic16F873A, LVP_OFF ' Low-Volt ICSP programming disabled

With any of PortB pins high the ADC will not respond until AN0 is above 0.063Vdc. If I ensure that all PortB pins are low the ADC responds correctlty.

I even added a 100 mS pause before and after issuing the ADCIN statement, that helped some, but didn't solve the issue.

In this aplication it's not a problem. I ensure that all pins on PortB are low before reading the ADC. The ADC now correctly reads 1 count for every 0.0488 volts.

Thanks,
Ron