Jelmer Vernooij has developed a command-line programmer for Atmel AT89S8252 parts connected via the serial port. The newest version of the program, called at89prog, can read, write, and erase code and data memory, lock the memory, or alter single bytes of memory. Jelmer has also written a protocol analysis (PDF format) to help other Atmel hackers. at89prog is Free Software licensed under the GNU GPL.