Keypad Library

The mikroPascal PRO for 8051 provides a library for working with 4x4 keypad. The library routines can also be used with 4x1, 4x2, or 4x3 keypad. For connections explanation see schematic at the bottom of this page.

Note: Since sampling lines for 8051 MCUs are activated by logical zero Keypad Library can not be used with hardwares that have protective diodes connected with anode to MCU side, such as mikroElektronika's Keypad extra board HW.Rev v1.20

External dependencies of Keypad Library

The following variable must be defined in all projects using Keypad Library:	Description:	Example :
`var keypadPort: byte; sfr; external;`	Keypad Port.	`var keypadPort: byte at P0;`

Keypad_Init

Prototype	procedure Keypad_Init();
Returns	Nothing.
Description	Initializes port for working with keypad.
Requires	`keypadPort` variable must be defined before using this function.
Example	// Initialize P0 for communication with keypad var keypadPort : byte at P0; ... Keypad_Init();

Keypad_Key_Press

Prototype	function Keypad_Key_Press(): byte;
Returns	The code of a pressed key (1..16). If no key is pressed, returns 0.
Description	Reads the key from keypad when key gets pressed.
Requires	Port needs to be initialized for working with the Keypad library, see Keypad_Init.
Example	var kp : byte; ... kp := Keypad_Key_Press();

Keypad_Key_Click

Prototype	function Keypad_Key_Click(): byte;
Returns	The code of a clicked key (1..16). If no key is clicked, returns 0.
Description	Call to `Keypad_Key_Click` is a blocking call: the function waits until some key is pressed and released. When released, the function returns 1 to 16, depending on the key. If more than one key is pressed simultaneously the function will wait until all pressed keys are released. After that the function will return the code of the first pressed key.
Requires	Port needs to be initialized for working with the Keypad library, see Keypad_Init.
Example	var kp : byte; ... kp := Keypad_Key_Click();

Library Example

This is a simple example of using the Keypad Library. It supports keypads with 1..4 rows and 1..4 columns. The code being returned by Keypad_Key_Click() function is in range from 1..16. In this example, the code returned is transformed into ASCII codes [0..9,A..F] and displayed on Lcd. In addition, a small single-byte counter displays in the second Lcd row number of key presses.

program Keypad_Test;

var kp, cnt, oldstate : byte;
    txt : string[6];

// Keypad module connections
var keypadPort : byte at P0;
// End Keypad module connections

// LCD pinout definition
var LCD_RS : sbit at P2_0_bit;
var LCD_EN : sbit at P2_1_bit;

var LCD_D4 : sbit at P2_2_bit;
var LCD_D5 : sbit at P2_3_bit;
var LCD_D6 : sbit at P2_4_bit;
var LCD_D7 : sbit at P2_5_bit;
// end LCD pinout definitions

  begin
    oldstate := 0;
    cnt := 0;                                // Reset counter
    Keypad_Init();                           // Initialize Keypad
    Lcd_Init();                              // Initialize LCD
    Lcd_Cmd(_LCD_CLEAR);                     // Clear display
    Lcd_Cmd(_LCD_CURSOR_OFF);                // Cursor off
    Lcd_Out(1, 1, 'Key  :');                 // Write message text on LCD
    Lcd_Out(2, 1, 'Times:');

    while TRUE do
      begin
        kp := 0;                                // Reset key code variable
        // Wait for key to be pressed and released
        while ( kp = 0 ) do
          kp := Keypad_Key_Click();             // Store key code in kp variable
        // Prepare value for output, transform key to it's ASCII value
        case kp of
          //case 10: kp = 42;   // '*'   // Uncomment this block for keypad4x3
          //case 11: kp = 48;   // '0'
          //case 12: kp = 35;   // '#'
          //default: kp += 48;

            1: kp := 49;  // 1           // Uncomment this block for keypad4x4
            2: kp := 50;  // 2
            3: kp := 51;  // 3
            4: kp := 65;  // A
            5: kp := 52;  // 4
            6: kp := 53;  // 5
            7: kp := 54;  // 6
            8: kp := 66;  // B
            9: kp := 55;  // 7
           10: kp := 56;  // 8
           11: kp := 57;  // 9
           12: kp := 67;  // C
           13: kp := 42;  // *
           14: kp := 48;  // 0
           15: kp := 35;  // #
           16: kp := 68;  // D

        end;//case

        if (kp <> oldstate) then         // Pressed key differs from previous
          begin
            cnt := 1;
            oldstate := kp;
          end
        else                             // Pressed key is same as previous
          Inc(cnt);

        Lcd_Chr(1, 10, kp);              // Print key ASCII value on LCD

        if (cnt = 255) then              // If counter varialble overflow
          begin
            cnt := 0;
            Lcd_Out(2, 10, '   ');
          end;

        WordToStr(cnt, txt);             // Transform counter value to string
        Lcd_Out(2, 10, txt);             // Display counter value on LCD
    end;
  end.

HW Connection

4x4 Keypad connection scheme

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