I am using the 10-bit A/D converter in the PIC16F877 to digitize 2
signals at a rate of 2000 samples per second for display on an LCD
screen. I seem to always have about 10 counts of noise even
when I put a large capacitor bypassing the RA0 and RA1 input pins
to ground.

I am using a 16 mHz clock frequency that I can't reduce.

I think I am following the datasheet recommendations:

tad=32Tosc
low impedance drive from an op-amp
wait 20uS between reading RA0 and RA1
.1 uF bypass caps near the chip power pins.
LM336 - 2.5 volt reference on RA3 bypassed with 10uF
software is written in CCS-C and uses the built in read_adc()
function

Is there some secret to getting true 10-bit accuracy. I don't even
have 8-bit now.

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