Dear Gabriel:
to send out a full package of DMX signal there's many thing need to be tacking care of.and if you try to make your dmx running in 40 reflash rate , forget it some of the fixture just don't work that fast, 20 -- 25 reflash rate will works for most of the case.
i had done it before, above suggestion may work for you , and that's what a did for my owm made console ( 512 channel * 2)
1. set uart in 8 bits model 1 by timer2
2.set timer1 as fram base ( 44Usec *2 or * 3)
3. enable timer1 first, tr2 next
4. set break time about 44Usec *2 or * 3 (by setting txd pin low without disable the UART)
5. 8 usec of MAB (just set txd pin =1 )
6.set and send starting code="0"
7.send out your channel data in timer1 interrupe
8. set dptr as your channel counter, compare this value in your uart interrupe, if dptr=512 then goto MPB
9. for MBP, just set txd pin =1 about 6msec or greater
10. after that return to step 4.
11. have fun
Chris chang