ATTINY 84 Aref pin?

Question

I want to program an ATTINY84 microcontroller using Arduino UNO as an ISP. In my program I need to use the AREF pin that is located at pin P0 on ATTINY84. I know that I can call analogReference() on Arduino UNO ATMEGA328, but what about the ATTINY84? Do I have to program the IC with some fuses?

Answer 1

For reference, here's a link to the ATTiny84 datasheet.

Section 16.13 specifies the ADC-related registers for controlling the ADC peripheral.

16.13.1 specifies the ADMUX register:

Bit 7 6 5 4 3 2 1 0
0x07 (0x27) REFS1 REFS0 MUX5 MUX4 MUX3 MUX2 MUX1 MUX0

If REFS1=0 and REFS0=1, the ADC will use the external reference on pin PA0.

These registers can be modified in code, here's an example using AVR-C:

ADMUX = 0x40;

Note that this will mess up the MUX settings, there are other ways to do this if you don't want to mess up the mux settings using bitwise operands:

ADMUX = (ADMUX & 0x7F) | 0x40;