How to use d0 and d1 pins of arduino uno (Others) as a digital output when I don't want to use Serial

Question

I have searched this topic almost everywhere also got different results that couldn't satisfy me

My new project is a 4x4 LED cube

Of which

Will contain 4 Rows and each Row will contain 16 LEDs

So, I need to use all the digital pins 0-15 as digital output.

And other pins 16-20 for grounding.

But the problem is, this project needs d0 and d1 pin to be connected as a digital output pin. (Not Serial communication)

In some places I have seen that Experts saying

1. If you want to use Serial communication, then you can't use them.

2. You can't use it while your arduino is connected to PC.

3. You Can't do this ,as this may harm the device

4. You must turn off serial connection first.

OK, reading this, I got confused, I don't need to use any serial connection (console and others) in this LED cube project so I tried to turn off serial connection by not writing the code below.

Serial.begin(9600);

So, will that free those d0 and d1 pins as digital for me ? Or USB connection is also considered as a serial connection?

So, how can I do it? And will doing it really harm my board?

Answer 1

If you don't use the serial port, pins 0 and 1 are regular I/O pins. It's just as simple as that.

If you want to use Serial communication, then you can't use them.

Correct.

You can't use it while your arduino is connected to PC.

Wrong. You can keep the USB cable connected as a power supply. You will not be able to use it for communication though.

You Can't do this, as this may harm the device

What is “this”? The device can be harmed if you drive too much current to/from an I/O pin, irrespective of whether it's a pin that could be used for serial communication.

You must turn off serial connection first.

Only if you did turn it on before. If you never enable Serial, you don't have to do anything more.

Answer 2

The bootloader always turns UART0 on upon the loading of the code to your Arudino Nano. So at the end of the day pins D0 and D1 are used for their alternate functions as a UART receiver and transmitter without you doing so in your code.

Copy the following code to whatever your sketch or C program to disable the UART0 module before you initalize pins d0 and d1 as digital IO, then you can set the two pins as digital I/Os as usual and they will work perfectly.

UCSR0B &= ~(1<<3);
UCSR0B &= ~(1<<4);