Waqar Zaka wrote:
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"further is there any window based shareware which can be used for linker, simultor and assemler purpose ?"

Look at the links on the left: Pinnacle52 and Raisonance, they aren't shareware, but offer limited (Raisonance up to 4k of code, Pinnacle I think that 4k also) for non registred use.

"Also how i can check that 400Hz square wave is generated upto 20 seconds on the simulator as i can only see that how much the time has passed ?"

put a break-point when you start the UP time of the wave, write the time showed in the simulator (Raisonce, I don't know if Pinnacle has that feature), continue the program, another break when the UP time ends, read the timer and do the math. The same for the LOW time, so yoou can be sure that your wave really is square. Or use an oscilloscope and see if it's ok.

hth