Making my own UART

Good evening,
I have a project in which I am supposed to create my own UART between 2 arduino UNO boards. The problem is that I am not allowed to use any of the following:

I/O pins 0 and 1 (assuming an Arduino Uno),
IIC,
SPI,
SoftwareSerial library.

I looked online on how to start this but everybody seems to be using Rx and Tx which I am not allowed to.
Could someone give me an idea on how to start my project ? Also, how could I set the baud rate without using Serial.begin() ?

Thank you.

copy out SoftwareSerial code

I am not allowed to use it.

look how is it implemented

RazvanAlbisoru:
I am not allowed to use it.

It sounds like you want someone here to give you a program that you have not been forbidden from copying.

Something tells me that your teacher wants you to figure out how to do it by yourself and learn something in the process.

...R

I suspect the idea is that you implement the equivalent of some SoftwareSerial function "from scratch."
Hopefully, class material and/or reading will have explained some of what that means. If not, you might start with Universal asynchronous receiver-transmitter - Wikipedia