The Mega 2560 board has several amenities for communicating with a pc, Yet another board, or other microcontrollers. The ATmega2560 provides four hardware UARTs for TTL (5V) serial communication. An ATmega16U2 (ATmega 8U2 about the revision one and revision two boards) about the board channels one of those about USB https://ligamega2557923.theblogfairy.com/27590650/details-fiction-and-liga-mega25