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Keypad Scanner

Verilog code for scanning and debouncing a four by four matrix keypad. Implemented on an Altera Cyclone FPGA development board.

The key pad decoder module assumes a normal telephone layout plus an additional column for A - D.

1 2 3 A
4 5 6 B
7 8 9 C
* 0 # D

Each key has a 4-bit address of the form Col:Row.

Key 1 2 3 A 4 5 6 B
Address 0000 0001 0010 0011 0100 0101 0110 0111

Additionally, it is assumed in the scanning (debouncing) module that the keys are normally disconnected and are pulled low when pressed (i.e. that they keyboard is not powered).

Usage

The keypad interpreter module has three outputs and one input,

Ouputs

  • KeyReady goes high when a key is ready to be read and does not go down until KeyRead goes high.
  • PressCout is the single hexadigit value describing the number of times the current key has been pressed, it is used to reaffirm the DataOut value if KeyReady is not being watched.
  • DataOut is the single hexadecimal digit (0 to F) value describing the button most recently pressed. Star is valued as "F" and Pound as "E".

Inputs

  • KeyRead must be asserted high for the scanner to continue. The KeyRead signal may only stay high for 8ms at most, it is recommended that the signal not remain high for longer than 4ms.

FYI

Below are issues that some folks have been kind enough to point out, I have not implimented them as I have no way to test and verify them.

  • On the decoder unit, the out variable is set to 7 bit lengths but only 4 bits are used.

  • It has been confired that the "waitbit" is needed. While I poorly (read: didn't) document what it is for, I am told that it insures that keypresses are recognized at the right time. I'm sure testing with the variable always set high will reveal make it clear to anyone with a dev board and keypad.

  • Tested on Intel DK-DEV-4CGX150N, Artyv s7, and others.

Contact

If you have questions, concerns, or comments please feel free to contact me via

[email protected]

License

Copyright (C) 2014 Adam Nunez This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See theGNU General Public License for more details.