"Honey, my PIC ADC pin sagged my peak detector voltage!"

[Jerson]

Yes I know 5V = 255, but what I was getting at...until I set all the portC pullups disabled (which they should have been at power up anyway), in the absence of an incoming analogue signal, I was geting an ADC reading of 255 (because there was 5V residual on the unconnected pin)...soon as I disable pullups, I got the reading I was expecting ...ie an ADC reading of 0.

This is expected behaviour. Pullups will put 5V on the ADC input. Unless you meant to ask something else.....

[HankMcSpank]

This is expected behaviour. Pullups will put 5V on the ADC input. Unless you meant to ask something else.....

That's just it - I never asked for or wanted pullups on the ADC pin, so was puzzled when 5V appeared there in the absence of a signal. The datasheet say WPUs are disabled at power up (& my code didn't enable them), so there shouldn't have been 5V on the ADC pin.....what I had to do in the end was disable them myself in my code - even though they should be disabled by default.

In my opinion there's a problem with the PIC16f1828's startup settings vs what Microchip say in their associated datasheet.

[rmteo]

In my opinion there's a problem with the PIC16f1828's startup settings vs what Microchip say in their associated datasheet.

Why don't you contact MCHP, inform them of your findings and have them confirm that the datasheet is in error (or perhaps the datasheet is correct and that you may have discovered a silicon error)?

[HankMcSpank]

Why don't you contact MCHP, inform them of your findings and have them confirm that the datasheet is in error (or perhaps the datasheet is correct and that you may have discovered a silicon error)?

For a few minutes I was overwhelmed by the onset of "global community spirit" to do the right thing ...so visited Microchip's website ...they've even produced a video about how to report back silicon errors.....I grew a beard to rival the guitarists in ZZ Top watching it, & then threw my wife's purse at the screen when it got to the bit about "& having followed the 11 steps we've just outlined, unless you attach scope traces we won't believe you & just assume you're a pleb"

I'm now hoping anyone similar 16f1828 problems will find this thread via Google.