454 B
454 B
This pin doubles up as the UART transmit pin, thus the name TXD. It's also commonly known as "Serial" and, by default, will output a Console from your Pi that, with a suitable Serial cable, you can use to control your Pi via the command-line.
UART is also extremely useful if you want to talk to Arduino or Propeller boards from your Pi, but you must make sure you disable the Serial Console in raspi-config first.