This may be a duplicate post.  Never received my copy so am posting again.


For some time I've felt that the ADC on the PIC16F87X were not really stable,
so today I decided to find out.

Using a 16F877 I applied a DC voltage to PortA.1.  I set ADCON1 for left
justify  - 65535 count max - and the count was jumping from 100 to 200 counts.  I
reset ADCON1 to right justify - 1023 counts max - and the count was jumping
about four.  This is equivalent to a fluctation of about 20mv.

I performed the same test with a 12-bit TLC2543 - 4095 counts max - and the
count was absolutely rock steady.  I checked both ADC voltage inputs with my
Optascope and there was no difference in either case.

20mv doesn't sound like much but when you are trying to control the ADC
output to plus or minus 5mv it's a bunch.

Has anyone else noticed this problem?

Sid

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