there's a new problem now that i ahve managed to get the waveforms.i have get the wavefrms as per the frequency or time period entered.......but how do i calculate the TH and TL for the timers in this case.......i mean what values do i lad in TH and TL f the timers.....as the time interval entered through a keypad varies evrytime.....how will the 8051 know what values to load into TH and TL....in shrt,how does the 8051 perform this operation.......kindly help.....i am due to submit this soon...very soon.