The communication we presumed to establish is done by a BAUD rate of 9600 bits per second. So for UNO to establish such baud rate and to start serial communication we use command ”Serial.begin (9600); ...

If so, it absorbs the program code from the computer and transfers it into the AVR chip, in a specific location so as not to overwrite the bootloader. If the computer isn’t trying to upload any code, ...

Now you already have an Atmega 328 chip with the boot loader. Next step is to program this chip using an Arduino board as an ISP programmer. Open the Arduino sketch which you want to upload. Connect ...

The code is written in pure AVR C, and full instructions for compilation are provided. Storage comes from an SD card, as the ATmega’s meagre 32k is nowhere near enough.