The Mega 2560 board has a number of services for speaking with a pc, Yet another board, or other microcontrollers. The ATmega2560 presents four hardware UARTs for TTL (5V) serial conversation. An ATmega16U2 (ATmega 8U2 over the revision 1 and revision 2 boards) to the board channels one of those https://mega2579135.liberty-blog.com/28026828/considerations-to-know-about-ligamega25