TTL port

From FIRSTwiki

The "TTL port" is a serial port which is configurable for either synchronous(transmission timing is controlled using a clock signal from a master) or asynchronous serial operation.

The TTL serial port is useful for interfacing to a number of things including other microprocessors and a variety of sensors.

For further information on using the TTL serial port, see the PIC18F8520 datasheet and the C18 compiler library reference. Both can be found at the Microchip website.