RS232enum. When you are presented with pins that you suspect provide Serial but you do not have access to the documentation. Connect your Arduino to all of the pins (limited by the number of Ditial pins you have on your board) and this sketch will try every possible pin combination and baud rate to determine RX/TX. It will also try to send wakeup characters to stimulate the line, such as a carriage return or other txpatterns that you add. This code sends data using a custom SoftwareSerial library.