i want to do a" timer project based on 16f84a"
and i want to use a single switch, mcu should be at rest before the switch is pressed and while the mcu is working if the same switch is pressed the program should be paused and it should resart when the same switch is pressed again
First of all you should start with timer module. Then go for the part containing the switch programming. Run timer module alone. Read datasheets and go through the timer peripheral. And then describe here some more details of your project.
#mcu should be at rest initially
#when the switch will be pressed timer program will execute and timer will be on
#then if the same switch is pressed timer should be paused
#and start from the paused point when the same switch i pressed again