For the sake of completeness:
| ARDUINO_USB_CDC_ON_BOOT | USB_MODE | UART (RX/TX) |
USB (native) |
|---|---|---|---|
| 0 | 0 | Serial HardwareSerial |
n/a |
| 0 | 1 | Serial HardwareSerial |
USBSerial HWCDC |
| 1 | 0 | Serial0 HardwareSerial |
Serial USBCDC |
| 1 | 1 | Serial0 HardwareSerial |
Serial HWCDC |