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Need guidance on 4x4 keypad interface

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Jun 7, 2011
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Hi guys.

Ok i have been googling and looking up in the forums for days but i still am very unsure about keypad interfacing. I want to design a 4x4 keypad decoder in FPGA using vhdl, and then display it on the 7 segment led of my nexys 2 spartan 3e board.

When pressed, ie: 5, on the keypad, the 7 segment should show a 5.

I understand that a 4x4 keypad has 4 inputs and 4 outputs (row and column) but how do i go about scanning which keys are actually detected? I've seen this term called like "de-bounce" but i totally has no idea what it really does. Also, how do i know which 2 pins of the keypad are for which push buttons?

I'm really confused on what i should do. Do i need a block diagram to implement this so that it'll be easier for me to understand?
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interfacing keypad with microcontroller: **broken link removed**

Lets say i have a row - R0,R1,R2,R3 and column - C0,C1,C2,C3 (to scan which keys are pressed) and i tie all the rows to high impedance, '1', while columns, i have it running using shift register (ie; 0111, 1011, 1101, 1110).

I was told that i will need a ring counter too but the thing is im lost, after reading up on ring counter. Ring counter works entirely like a shift register isn't it?

can anyone correct me if i'm wrong? anyone, enlighten me please....

--Edit with block diagram uploaded.



*YellowCircled - Column
*RedCircled - Ring Counter
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ok i supposed the ring counter in the block diagram are used for my 4-digit 7 segment. Does it sound right, anyone?

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