SLIP is a protocol for sending packets from one device to another. Itís incredibly simple and a handy protocol to use when communicating with embedded devices. While I have seen libraries for TCP/IP over SLIP for Arduino and Microchip, for a lot of applications this is more than is really needed. For a microchip with very limited memory not using TCP/IP can mean having a lot more space for the user application. While I have written the library for Arduino itís so simple it can be modified for other microcontrollers (I used to use the same sort of thing for Microchip microprocessors).
For echoing back the packets an Arduino can run the following code.
A Qt program that runs on a PC connected to the Arduino could run something like the following.
For a more useful example of using this library see http://jontio.zapto.org/hda1/JDDS.html which uses this library to create a square wave signal generator with a nice GUI. Also see http://jontio.zapto.org/hda1/BPSK_test_on_DDS.html which uses the SLIP library to use a DDS module for modulating BPSK in a test.