Keypad matrix with 8051 micro help

Discussion in 'Programmer's Corner' started by CALcircuits, May 12, 2009.

  1. CALcircuits

    Thread Starter New Member

    May 5, 2009
    3
    0
    I have found a sample code for an 8051 microcontroller and programming it to read a keypad matrix. I need a little help understanding the code. Here is what i found:

    here is the link to the code, i am just looking at the assembly code:

    http://www.8051projects.net/keypad-interfacing/8051-programming.php

    And I found the instruction set here:
    http://www.atmel.com/dyn/resources/prod_documents/doc0509.pdf

    I am having trouble understanding what the keyval equ 30H is doing and how the rows are being read from this. Is the, pressed bit 0H, just an assigned variable.
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The first link you posted is not working.
     
  3. AlexR

    Well-Known Member

    Jan 16, 2008
    735
    54
    The program set a variable keyval hold the key number, I would assume the 30H is the location of keyval (I'm not realy up with 8051 assembler).

    It then puts a low on the first row and scans through the columns looking for a low.

    Each time it fails to find a low it increments keyval.

    It then put the low on the second row and repeats the process.

    And so on until it either finds a low key or it comes to the end of the keys.

    When it find a low it waits for the key to be released (a high) and ends, keyval will contain key number that was pressed.
     
    Last edited: May 15, 2009
  4. Arm_n_Legs

    Active Member

    Mar 7, 2007
    183
    10
    keyval equ 30H: This 30H refers to internal data memory location 30H. In this context, it is just a location to store the variable keyval.
     
  5. rushi53

    Member

    May 8, 2009
    21
    0
    keyval equ 30H
    it means wherever keyval word occurs, replace it with 30H
    this command has 2 purpose
    1) it gives readability to program, by this I mean, u can understand the meaning of pins/memory used for
    2) it gives quick replaciblity - this means u can replace any pins/memory very quickly

    let me know if you need more explanation


    --------------------------------------------
    Thanks,
    Rushikesh
    www.projectsof8051.com
     
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