I use the timer interrupt to run the uart transmit routine in all my products that have to transmit DMX (lighting control datastream). DMX calls for a break to identify the start of the frame. Trying to sync the break with the uart transmit with the transmit holding register just became too much of a pain. Using the timer interrupt, dumping a byte into the txreg means that byte starts transmitting right now. There is no other byte currently in the shift register. That works nicely. Doing the break on the PIC is a bit of a pain. In most products I use another pin that is connected to the tx output through a resistor. That pin is normally tristated. When I want a break, I program that pin low (pulling the serial data from the pin that I tristate instead of from the tx pin on the PIC).

Harold




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