pic16f887 analogue reference

[spuffock]

Am I correct in assuming that I can read the 600mV reference on address 1111, and use this to determine the true VCC?

 

[eng1]

Am I correct in assuming that I can read the 600mV reference on address 1111, and use this to determine the true VCC?

Yes, select Vdd as the reference to the A/D converter and the 600 mV reference as the input (setting CHS0/3, as you said).

 

[Pommie]

Good find. I have a project at the moment where this would be useful. The data sheet is a little unclear as to how this can be used, it appears that the only place that the Fixed Vref goes is to the ADC input - is this correct? I'll probably get time tomorrow to try this but just thought I'd ask (it's midnight here). The reason I ask is because I'm using the comparators with the ladder Vref and the diagrams in the data sheet suggest that this would still work to measure Vdd.

Mike.

 

[Mike - K8LH]

I believe there's an application note that specifically describes using the hardware for that function. I'll see if I can find it for you Mike.

Mike


<added>

It's application note AN1072A - Measuring Vdd using the 0.6v reference

 

[Pommie]

Hi Mike,

Thanks for the AN, that will come in useful tomorrow. It doesn't however answer my question, can you have both the ladder Vref and the Fixed Vref at the same time. I.E ladder to comparator inputs and fixed to ADC input.

Mike.

 

[eng1]

it appears that the only place that the Fixed Vref goes is to the ADC input - is this correct?

The fixed Vref can be used as the reference to for the comparators too. CVref and the fixed Vref are multiplexed (see bits C1Rsel and C2Rsel).
Also, CVref can be selected as the input of the A/D converter according to the datasheet (ADCON0, CHS0/3).
I haven't used both at the same time but I agree with you, the diagrams in the datasheet suggest that it's possible.

The reason I ask is because I'm using the comparators with the ladder Vref and the diagrams in the data sheet suggest that this would still work to measure Vdd.