The Mega 2560 board has a number of services for speaking with a pc, A further board, or other microcontrollers. The ATmega2560 supplies 4 hardware UARTs for TTL (5V) serial conversation. An ATmega16U2 (ATmega 8U2 around the revision 1 and revision two boards) within the board channels one of those https://liga-mega2525791.activablog.com/27574448/the-smart-trick-of-mega25-that-no-one-is-discussing