I have an Arduino Project developped for an UNO Arduino Board; the sketch have a size of 30000 bytes aprox.

The whole set of features requeried works perfectly, but I have a problem with the A0 pin

In input mode Early, on the project developement, I tried to use the A0 pin to read three buttons linked with resistors; after many issues, a change to the pin A1 solved the problem.

In output mode On a later phase of the project, when I have occupied the rest of pins, I need to sent digital signal by the A0 pin... really the signal is sent by a function that send to digital 2, A2 and A3 pins also; but as in the referred pins the signal it's constant, on the A0 pin seems flickering

I tried to change many questions of the software, but isn't effective. So, this occurs on three UNO original boards and three selfmade boards with the chip and the bootloader uploaded -the A0 pin incorrect on the board it's statistically discarded ;) -

Any idea to resolve this?


The A0 output (aka PC0) on the Atmega328 works for everyone else, so the issue is either in your software, or in what you have connected to it. To eliminate the software aspect, start with minimal code which sets the output high and leaves it there:

void setup () {
   DDRC = 1;
   PORTC = 1;
void loop () { }

If the flickering occurs then the issue is hardware, and you need to tell us what is connected to it. If the flickering does not occur then the issue is software, and you need to tell us what software is running.


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