I've created this for my final project, just before I graduated in Electrical Engineering. The system uses a PIC16F428 and all the code was done directly in assembly. Nowadays I would not bother to program in assembly :)
It worked connected through the serial port (2400-8N1). Each command started with a '@' followed by the line number (1 or 2) and the text (maximum 12 characters).
Example: @1HELLO, WORLD!