Interrupt Triggered KeyPad

[Paradigm]

Dear All,

I have a 4x4 keypad and wishes to put my MCU to sleep. Therefore I am thinking of having an interrupt triggered scanning keypad instead of doing constant polling.

How should I connect the hardware of the keypad? How many interrupt do I need? What must I do inside the service routine to detect the keypress

Thanks a lot for any help.

 

[barry]

You don't give us enough information. What is your hardware? If you are using a 4x4 keypad then, assuming there is no extra circuitry, you will need at least 4 interrupts: All four rows are driven high, and the four column inputs would be interrupts. But you will still need to do a scan after the interrupt occurs to determine which of the four switches in the column was pressed.

If you are willing to use extra hardware, then there are other approaches.

 

[zuisti]

Hi Paradigm;

If your proc has PORT Change Interrupt (at least on 4 pins like almost all PICs on PORTB) and it can wake-up from SLEEP (see your datasheet) then it is possible using only one interrupt (this).

For example set all 4 keypad columns to zero and pull up (as usual) the rows to VCC. If the 4 rows are connected to the 4 input pins capable PORT Change Interrupt, interrupt occurs (the proc returns from SLEEP) when any key pressed, because the PORT (any of the 4 pins/bits) is changed.

Then, as barry wrote, you will still need to do a scan (even in the interrupt routine) to determine which switch was pressed.

A word of advice: use a short delay (15..20 msec, for debouncing) before scan the switches.
zuisti

 

[Paradigm]

Hi Zuisti, which model of PIC provide PORT change interrupt? Can advise? Thanks a lot

 

[zuisti]

Hi Zuisti, which model of PIC provide PORT change interrupt?

As I wrote almost all (14+ pins) PICs have this feature (on PORTB.4...7).
For example:
PIC16F628A, F87, F88, F877A ...
PIC18F2620
an so on

 

[barry]

Hi Zuisti, which model of PIC provide PORT change interrupt? Can advise? Thanks a lot

I think it's time for you to actually read the documentation.

 

[dolqiu]

thanks for all the information guys

jual beli
iklan gratis