ADC Channel Measurement Using Internal Reference

[Brian1]

Is it possible to use the ADC to measure the voltage on an external pin and use the internal reference at the same time? I have a product that is direct connected to battery, so my external reference voltage is variable. I'd like to use an external channel to measure a voltage, but use the internal reference. Are there any examples that exist for this?

[Vyacheslav Azarov]

In simplest form you can use this formula: Vrin = Vref * Dain / Dref , where Vrin - real input voltage, Vref - known voltage of reference source, Dain - conversion result of analog input , Dref - conversion result of reference source voltage.