using 89C2051, the GND pin is open but still program is working.

I m using AT89c2051 and using DS1232 to reset the microcontrolller in failed condition. Microcontroller has to give some pulsed signal to DS1232. In any fault condition if microcontroller is nt working, then it will not give the pulsed signal to DS1232, then DS1232 will reset the microcontroller. But here in my circuit if ground pin is open still microcontroller is giving singal to DS1232. and remaining pins are going high....

You need to disconnect the ground line from the circuit. Any pins tied to ground will provide an alternative path and keep the chip running.

Mike.

actually for testing i broke the GND leg of the microcontroller.... and i m giving ground to GND pin externally by wire while switching it ON. aftr that i m removing the ground wire from the GND leg of microcontroller, but still the program is wrking...

I have connected ground with crystal also.... through capacitors, is it possible that microcobtroller is getting ground from there...

You must have a pin that is active low and that is making a ground path to power the chip. You must make the break between the power supply and the circuit of the micro. Why not read a push button and go into an infinite loop when it's pushed?

Mike.