Hi Phillip... Thanks for your answer... I used your code instead of mine... the problem persists...

I really dont know why this happen, only thing comes in my head now is this yamaha has a slightly different baud rate (maybe I'm wrong) that makes it incompatible with the 8051 at 12mhz... because the circuit works in all other midi devices I connected until now including my other 8051 midi projects, 3 keyboards, 2 sound cards and 1 midi-usb interface.

Another strange thing, I already connected another of my midi projects that OUTPUTS midi data to this yamaha and it worked normally, maybe it was not a big amount of midi data.

Also made another test... I connected in the inverse direction... computer outputs 8051... 8051 outputs to keyboard... and the keyboard outputs back to pc ... I think an equivalent problem happens, it misses many commands, also played a midi file and PC and it became the worst music I ever heard!