My 12lf1822 ADC won't read zero (lowest reading is 008)

[HankMcSpank]

well, I got to the bottom of it...something whacky going on here!

It's something to do with the way I'm setting the weak pullup register....

Firstly, I noticed that when I disabled weak pullups (I just took a flier!)

OPTION_REG.7 = 1 ' disable weak pullups

My ADC started reading down to zero as it should!

Sure enough when I enabled weak pullups again, the problem returned.

But this is where I’m obviously doing something wrong, this way actually works…

(I want weak pullups of RA3)

WPUA  = %00001000 
IOCAN = %00001000 

…ie even with weak pullups enabled my ADC reads down to zero.

But if I do this….

WPUA.3 = 1
IOCAN.3 = 1

My ADC won’t read down below 008 again!

So to get ADC reading down to zero *with* weak pullups enabled on a 12LF1822, it must be set like this....

OPTION_REG.7 = 0
WPUA  = %00001000 
IOCAN = %00001000 

Not sure if it makes any difference but my weak pullup is on the MCLR pin.

Anyway, I'm happy - it's sorted!