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05/29/06 08:05
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 		 #117215 - derivative with interrupt on pin change
Responding to: ???'s previous message
If you can find a derivative with interrupt on pin change, you can do this with no additional hardware devices.

I usually do this on the PIC (sorry folks) to wakeup from sleep. How ? - On initialisation, I set the port (8 bits to scan a 4x4 matrix) to 0xf0 where the columns are set to F and rows are set to 0. Set the port columns to interrupt on change. Now, whenever a key is pressed, I get an interrupt. On seeing the interrupt, I scan the matrix to get the key/s.

This is a very effective way to wake up the CPU on a keypress and conserve battery power if you will.

Sorry to be very verbose, but I hope this helps. Perhaps you can find a derivative on Philips with an interrupt on pin change

Jerson

List of 28 messages in thread
TopicAuthorDate
passive matrix keyboard readout            01/01/70 00:00      
   yep use the dallas switch debouncers            01/01/70 00:00      
      really, you can't have it both ways            01/01/70 00:00      
   Keypad            01/01/70 00:00      
      what???long weekend maybe            01/01/70 00:00      
         dedicated HW in some '51s            01/01/70 00:00      
   watch human reaction speed            01/01/70 00:00      
   derivative with interrupt on pin change            01/01/70 00:00      
      Or use a maxim 6816            01/01/70 00:00      
         I use SW debouncing...            01/01/70 00:00      
   Can reduce time spent in ISR Key Scan            01/01/70 00:00      
   Use tiny slave micro            01/01/70 00:00      
      Makes sense!            01/01/70 00:00      
         Programming the slave micro            01/01/70 00:00      
            $0            01/01/70 00:00      
               Non-zero cost            01/01/70 00:00      
                  who cares            01/01/70 00:00      
                     The folks who pay will care            01/01/70 00:00      
                        You apply what I said about apples to or            01/01/70 00:00      
                           you missed my meaning            01/01/70 00:00      
                              OK, I'll clarify            01/01/70 00:00      
            Costs? He needs to solve it anyway...            01/01/70 00:00      
               Tme is money            01/01/70 00:00      
                  contradictory            01/01/70 00:00      
         Key bounce.            01/01/70 00:00      
            use a LPC            01/01/70 00:00      
               any MCU will work            01/01/70 00:00      
                  with a LPC you can do either            01/01/70 00:00      

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