For even more fun with low level breaking of standards, bit-banging rs232 is fun and very doable. Don't use timers for timing either, just spin the cpu the right number of times. :)
This project actually does decode of Rs232 data, with the special prefix triggering the interpreter mode where you can control the color and delay between the cycles. Only ground and TX pins are used to connect. Oh, and no interrupts - poll for the start bit while running the currently programmed light animation cycle :-)
One thing that made the development of it all immensely easier was having a Saleae logic analyzer. Highly recommend it (no affiliation, just a happy customer).
