Use internal vref in pic16f677

[gamersat678]

Use internal vref

I have a pic16f677 with a fixed internal vref of 0.6v. I figured out how to use vdd as the input for the adc but I want to use the internal volt reference. I've done some reading and I think you have to change ADCON0 to some value? Btw the data sheet for the chip is **broken link removed** and I program in mikrobasic. Any help is very much appreciated.

 

[btbass]

Re: Use internal vref

The adjustable 0.6 Volt nominal internal reference is primarily used by the on board comparators. It's value can be read by the A/D, but not used as a reference for an A/D conversion. If you need more accurate A/D conversions, feed an external ref voltage to the A/D Vref pin.

 

[cdh7]

Re: Use internal vref

Note, however, that you can measure the 0.6V reference with the ADC and use the result to solve for your ADC reference voltage Vdd.

For example, measure the 0.6V reference: res1 = 0.6V / Vdd * 2^10

Then measure an analog input: res2 = Ain / Vdd * 2^10

You can then calculate the analog voltage Ain = res2 / res1 * 0.6V independent of the supply voltage Vdd.

Regards,
Chris