Redwood Shores, 8 januari 2006. What you are describing sounds similar to a bootloader. I believe there are many solutions to do this, and I guess you could do it on the fly too. Be aware, though, that some 18F only allow you to overwrite the internal memory up to 1000 times, which could become an issue if you keep using this RS-232 solution to upload different functions. I think it would be better (if possible in your case) to just premake all the functions, and only upload a byte that indicates the location in a jumptable, and jump to the function that way. You might wish to elaborate a little bit more on what you're trying to accomplish. Greetings, Maarten Hofman. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist