Hello! The source code you need depends on Assembler you are using. What kind of assembler do you use (manufacturer)? I suggest you to visit www.atmel.com They have a lot of example programs absolutly free. I can also send you a guide book to Raisonance MA-51 (to your email, because pdf is too big) and some programs. But I am not quite sure if it is usefull for you. A few times ago I has asked my friend the same way. He give me the program, but since this time I could not use it. It is for another assembler. Easier way is to write a new one... I wish you good luck,
Jacek.