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interface between mcu and matrix keypad

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alaaalkhfagi

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hi interface 4*4 matrix keypad to the microcontroller by using 74c922 encoder but i cant figure out the loop require to scan key press and to hold the data "i am new to the microcontrollers"
 

I've designed and programmed with a 74C922 on an 8051 microcontroller. Which microcontroller are you using? Are you programming in C or assembler? Can you explain your question in more detail...
 

This encoder has an interrupt output. And your MCU also has an external interrupt input.(in PORT A in PIC) I think that you should use external interrupts with Low to HİGH edge. Otherwise you will probably get your number input several times.
 

I use two DS2408 to cover 4x4 keypad, connection between keypad and main board is far several meters, working over 1-Wire protocol and uses only two wires.
 

In Maxim website DS2408 costs $2.75 @1k so basically $5 for two pieces and seems expensive.
For that money I can buy four ATMEGA8 use one AVR in each side and keep the other two for the next project!
 

alexan_e said:
In Maxim website DS2408 costs $2.75 @1k so basically $5 for two pieces and seems expensive.
For that money I can buy four ATMEGA8 use one AVR in each side and keep the other two for the next project!
Click to expand...

Yes but then you dont need ATMega8 you can order finished working device from china for few euros. No need for making PCB, soldering, programming, ... :wink:
 

This is not what I'm saying , I'm basically can't understand why the cost of some port expanders or 1wire switch like you mention is so expensive when you can do the same job and even more with an mcu that costs half the price?
 

I understand your point but as tpetar mentioned, professionally you'd have to add the cost of writing the software to the part cost. The software engineering cost per day sure adds up. One could then see it as: of course the blank micrcontroller part is cheaper than a dedicated ready-to-go chip, the blank part doesn't do anything :)

Meanwhile, back at the keyboard decoder...

alaaalkhfagi, please can you sketch out your circuit with part numbers and post it, thanks.
 

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