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using ext. interrupt in at89s51

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saraheem

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Hi...

I am using AT89S51 uC. My proj requires the use of the external interrupt Int0 (pin 12 in the IC).

My doubt is: After switching on the power supply and resetting the circuit the Int0 pin goes hi automatically (Before reset the pin is low). But when i first implemented this on the bread board, it was in low state only even after the reset and i used to pull it hi manually to prevent it from going into the int service routine.

Will the interrupt work if i just pull it to ground??? Or will it damage the uC??? :?:

I checked with 2 different uCs having the same program... Both of them are reacting in this way...

Pls tell how to use this int...?

Thank u...
 

On power-on all I/O pins are set as inputs and pulled-up by internal (weak) circuit ..
ExtInt0 and ExtInt1 can be set to trigger an interrupt on the falling edge or low level, that mans that you can safely pull them down to the GND level and by doing so start an interrupt service routine – there is nothing dangerous in this action, pretty normal stuff ..

Rgds,
IanP
:D
 

Thank u IanP...

asked because earlier while doing it in breadboard i had to connect the ext int0 to Vcc to avoid it from going into the isr. Now it is having 5V(hi) after the initial reset on power up. Before reset its 0...
 

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