hello kunal rest through circuit is quite simple its just a RC combination
for software triggering use watchdog
here is the link for basic of watchdog
http://www.engineersgarage.com/embedded/avr-microcontroller-projects/avr-watchdog-timers-circuit
i am not good in asm … if any where you get a c code you can see its asm taranslation follow this link
http://www.engineersgarage.com/forums/8051/c-code-assembly-code