Internal Vref 18F67j50

championx · Joined: 28 Feb 2006 Posts: 151

Hi! im trying to configure the internal vref of a pic 18F67j50, but the adc reads always 1023.

Here is the config:

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

The internal Vref generator is intended for the comparators, not the A/D.

temtronic · Posted: Sun Jul 07, 2019 8:05 pm

I was curious, so I looked at the datasheet.
While it can't be used 'internally connected', you can access the Vref generator on pin RF5. You can connect that to the ADC Vref+ input pin ( AN3). That 'should' work, HOWEVER be sure to read the ADC specs for the allowable value Vref+ can be. That'll be in the back of the datasheet ( electrical specs...) Also you'll probably need to buffer the Vref output (that's in the datasheet too....)
It might be worth the 1/2 day to 'work it out, on the bench' to see if it'll do what you want. That all depends on your application.

Jay

dluu13 · Joined: 28 Sep 2018 Posts: 395 Location: Toronto, ON

Back when I used a couple of PIC16Fxxxx they had a fixed voltage reference (FVR) module that allowed selecting a 1.024, 2.048, or 4.096V internally generated reference for the ADC. It was convenient. I wonder why they didn't put that over to other PICs as well.

championx · Joined: 28 Feb 2006 Posts: 151

Hi! thanks for your answers... yes, sadly, this pic does not have FVR... I can't use the external Vref pin because its already mapped on the board.

I guess i should make a capacitor discharge time measurement to use this pin as ADC.

Thanks!