interrupt-on-change on 8051 microcontroller

Question

I am trying to read the speed or number of rotations pulses of a self-made encoder motor.

I am using an AT89C52 microcontroller. It gives external interrupt on rising or falling edge.

How can I attach both rising and falling edge interrupt in AT89C52?

• Mitu Raj: Well there is a bit in EX. interrupt register which you can set/reset to decide the edge
• Deepak Yadav: you are right IE SFR provides EX1 & EX0 to enable the external interrupt. but the problem is how to call isr ON pin change value of external interrupt pins.
• Mitu Raj: You dont need to call explicitly, it is implicitly called when interrupt edge occurs. You just set the registers and the write the definition of ISR as per the c52 compiler format.
• Mitu Raj: Not IE SFR. Thats only for enabling. For each external interrupt there are dedicated register. Did you find that ?

Answer 1

There seem to be TWO negative edge triggered external interrupts on that microcontroller. Take your signal, and send it to one interrupt input. Invert the signal, and send it to the other, and enable both interrupts.