Hi Marco

you are tring to see a waveform which is present one tenth of a millisecond when u transmit a byte u might be able to see it when u send continious transmission, check the frequency of the crystal against the value of the timer (it's easy if u use 11.0592mhz crystal as the value are given in most data sheets ) to see if ur controller is receiving the character u can make it to echo the character back try this peice of procedure
skip:jnb ri,$
mov a,sbuf
lcall tr
reti
tr: mov sbuf,a
jnb ti,$
ret

in line 1 skip u r statement is mov sbuf,a if u r receving a byte it should a,sbuf

best of luck