Fair enough. I know that much. Maybe I should explain the application. I have an external measurement chip with its clock output direclty onto P0.0 on my TI chip. Now, this port has a dedicated interrupt vector which i have enabled to interrupt on a HI/LO transition and there by count pulses. Can't use timers to poll the pin cos current consumption is crucial in this application. I know the theory behind it, but implementing it i do not know. I know that I want it to be.. lets say 0.1, so that for every 10 pulses I will get a value of 1, thats the division bit, and for multiplication is must be anything above 1, so it will be (prescaler x pulsecount). At the end of the day I am going to count pulses representing something, litres, kWh, whatever, and multiply/divide it by the pre-scaler value, and probably by a calibration value and then use this result for something. Also I think a floating point prescaler would be easier to set as a divide or multiply. So, the theory is all there, but i do not even know where to begin to implement it. do i use timers? how do i write the code for it etc. i have been told its the easiest thing to do, for i have completed the rest of the code, but hey, if u don't know something, u don't know it. Thanks once again.