Hello Forum,

In my project I am struggling with external interrupt 0. I am using AT89S8252 microcontroller, which is controlling a DC and AC motor. I want to use external interrupt 0 as emergency stop button. As in emergency stop, I want microcontroller to stop all operations in process and go back to start of program. As I switch on power to microcontroller, the code works fine and the external interrupt works fine as well. but as the program goes back to start and runs again , then the external interrupt does not work. Means external interrupt works only once after switching on power.In order to make it work again I have to siwtch off power and switch on again (which I understand resets the program) But why is that ?? I have read the tutorial and previous threads on website but could not figure out the solution. I am making the program to jump to start within interrupt routine, is this the problem?

Below is the code

Initialisation of Interrupt

START2:
MOV SP,#31H
MOV IE,#85H
CLR IT0


Interrupt Service Routine is as below

EXTERNAL_INTERRUPT:

      MOV P0,#0FFH
      MOV P1,#0FFH
      MOV P3,#4FH
      CALL CLEAR_LCD
      CALL EMERGENCY_STOP_TEXT
      
      LJMP MAIN
      
      RETI

All suggestions would be appreciated

Regards
James