What do you mean by use a key which has 3 points? And how can CPU logic perform real time during power down?

I am poor at making drawings, converting to GIFs and uploading. Sorry for that..

Any normal key has two points which are shorted together when you press it. I am talking about a key switch with 3 points which all would be shorted together when you press the key.

Now you can use the two points just as you normally use a switch. Make a matrix this way. Now every key has a third point which is floating. Connect all these points together and connect to CPU interrupt pin.


If no key is pressed, INT pin will remain high. If any key is pressed, this will cause the INT to go LOW.

I have seen some keypads in this fashion and used them. This works perfect..

Good Luck