8051 external interrupt INT0 issue


How do I write an ISR greater than 8 bytes which is triggered by INT0?

Best Answer

Your code jumps to the ISR which ends in a RETI:

    org 0003H
    jmp isr

    ; ...

    ; any instruction you need

If you program in C, this will be handled for you automatically. For example, Keil-C51 places ISRs right at the start address if there is enough room, or jumps to it if not.