Using the internal DAC in a PIC Micro

You have probably got a usable DAC (Digital to Analogue Converter) if your PIC micro has a comparator inside. The voltage reference module in the PIC micro lets you generate a programmable analogue voltage.

"Using the internal DAC in a PIC Micro."

You have probably got a usable DAC If your PIC micro has a comparator inside. The voltage reference module in the PIC micro lets you generate a programmable analogue voltage.

Inside some PICs there is a voltage reference and a comparator.

The normal use for the voltage reference is to connect it to one input of the internal comparator - the other input has the voltage you want the comparator to test.

But for some PIC microcontrollers you can
send this voltage to an external pin for your own use.

Note: Some PIC micros do not let you output the voltage reference to anexternal pin - you just have to read the datasheet (if the see CVRCONhas a control bit labeled CVROE)- if it does then you can use the DAC output.

Although the internal voltage reference is not that versatile (as it was not really intended for external use) it is free, programmable and ready to use.

It has a few limitations but the most important is that you can not drive high currents out so as long as it is driving a high impedance it will be OK.  
Note: If you need to drive more current just buffer it with an opamp.

Normal use of the DAC

The voltage reference module was only intended to generate a voltage for the comparator module but some devices include a control bit to output this voltage to a pin.  

Note: The comparator module is flexible and does not have to use the reference - it can also use the analogue input from a pin.  There's more information on using the comparator here.

Not all devices have this control bit so you have to look in the data sheet to check if your device will output the voltage.  See the next section to look at typical registers in the voltage reference part of the datasheet.

Note: This control was only intended for testing the reference generator but with careful use you can use it in your projects.

PIC DAC control registers

 

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