The communication to the USB is handled by the USART on most Arduinos. Converting the serial signals to USB chunks is done by a separate chip (FTDI for older Arduinos and most clones, an ATmega16U2 on the UNO and Mega2560).
The communication to the USB is handled by the USART on most Arduinos. Converting the serial signals to USB chunks is done by a separate chip (FTDI for older Arduinos and most clones, an ATmega16U2 on the UNO and Mega2560).