Accessing I/O in ATmega328P (Arduino) using Assembly and C - Hackster.io
The Pi & I: Programming the ATmega328P Registers From the Arduino IDE
Programming Atmega328p Microcontroller with Arduino IDE - Electronics-Lab.com
Difference between Atmega328 and Atmega328p
atmega - Can I use ATmega328 TX/RX pins to drive an R2R network and still use the serial port to program the MCU? - Electrical Engineering Stack Exchange
Amazon.com: diymore 5pcs Pro Mini ATmega328P 3.3V 8M Module Board with Crystal Oscillator Pins Replace ATmega128 : Electronics