What does C.0 do? does it flash an LED?

if its used for something else, then it might be a good idea to ad an LED and make it flash on and off as your program runs. I find that it helps me know where the program is getting hung up or if its running at all..

One other thing, and im not sure if its right or not, but wheni use an external osc i need to set it to HS not XT.