Hi!
thanks everybody
one more little question:
how can I get the timing for start/stop condition?
I have now wrote a code that is timed with NOP instructions, but obviously it isn't accurate at all.
my real question is: the clock with which the instructions are executed is that of internal clock (33MHz for AT89C55WD) or the clock driven from external (I am to put a 3.5716 cristal in XTAL1 leaving XTAL2 not connected)
in this way, how can I time startstop condition?

best regards,
teo.