3x3 keyboard interfacing with msp430

[skarthikshines]

hi,
i am beginner in programing. i tried to interface the keyboard with msp430 and i did successfully.. i referred some example circuit to interface keyboard. in one example they used pullup resistors with rows and column , and in second example they did t use the pull up resistors and in some other example they connect the column via diode and row with the pull up resistors.. i need to know what is the difference between this three example and which circuit will be a better one???

 

[bigdogguru]

There are numerous ways of interfacing a keypad to a MCU, even a single wire interface is possible.

Can you post the schematics of the three examples? So that we may examine them and discuss their individual pros and cons.

Most keypad interfaces fall into two categories, Polling or Interrupt Serviceable.

BigDog

 

[skarthikshines]

first one
second one
third one
and i did coding for first method and its working perfectly.. suggest me which one is good..

 

[betwixt]

They are all the same method - output one bit at a time and read back to see which input sees the bit.

There is another completely different method which most people overlook:
1. Drive all outputs high simultaneously,
2. Read back the inputs. Zero = no keys are pressed, otherwise...
3. Swap inputs and outputs over and drive the new outputs high simultaneously.
4. Read back the inputs.

You now have the row and column coordinates of the pressed key.
In PIC language it can be coded in very few instructions.

Brian.