hi,

OK i will play it using LED first. The port B0 that i declare says that when the fault signal detect 5V is the normal operation, when suddenly changes to 0v, port B0 automatically goes to my interrupt handler to do whatever need to be done.
So, my question is:

1. did portb0 can detect directly 5v without adding extra codes that define the values of voltages?
2. if yes, can i use pull-up resistor with push-up button to create a changes signal to the portb0 and see the interrupt works or not?
3. if not, what others method to create a changes signal to the portb0?

thanks,
photoelectric