Connect Keypad with 8051 code

The mikroC 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 :
extern sfr char keypadPort;	Keypad Port.	char keypadPort at P0;

Library Routines

• Keypad_Init
• Keypad_Key_Press
• Keypad_Key_Click

Keypad_Init

Prototype	void Keypad_Init(void);
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 char keypadPort at P0; ... Keypad_Init();

Keypad_Key_Press

Prototype	char Keypad_Key_Press(void);
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.
Example	char kp; ... kp = Keypad_Key_Press();

Keypad_Key_Click

Prototype	char Keypad_Key_Click(void);
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.
Example	char kp; ... kp = Keypad_Key_Click();

Code 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.

unsigned short kp, cnt, oldstate = 0;

char txt[6];

// Keypad module connections

char keypadPort at P0;

// End Keypad module connections

// Lcd module connections

sbit LCD_RS at P2_0_bit;

sbit LCD_EN at P2_1_bit;

sbit LCD_D4 at P2_2_bit;

sbit LCD_D5 at P2_3_bit;

sbit LCD_D6 at P2_4_bit;

sbit LCD_D7 at P2_5_bit;

// End Lcd module connections

void main() {

  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:");

  do {

    kp = 0;                                // Reset key code variable

    // Wait for key to be pressed and released

    do

      // kp = Keypad_Key_Press();          // Store key code in kp variable

      kp = Keypad_Key_Click();             // Store key code in kp variable

    while (!kp);

   // Prepare value for output, transform key to it's ASCII value

    switch (kp) {

      //case 10: kp = 42; break;  // '*'   // Uncomment this block for keypad4x3

      //case 11: kp = 48; break;  // '0'  

      //case 12: kp = 35; break;  // '#'

      //default: kp += 48;

      case  1: kp = 49; break; // 1        // Uncomment this block for keypad4x4

      case  2: kp = 50; break; // 2

      case  3: kp = 51; break; // 3

      case  4: kp = 65; break; // A

      case  5: kp = 52; break; // 4

      case  6: kp = 53; break; // 5

      case  7: kp = 54; break; // 6

      case  8: kp = 66; break; // B       

      case  9: kp = 55; break; // 7

      case 10: kp = 56; break; // 8

      case 11: kp = 57; break; // 9

      case 12: kp = 67; break; // C

      case 13: kp = 42; break; // *

      case 14: kp = 48; break; // 0

      case 15: kp = 35; break; // #

      case 16: kp = 68; break; // D

    }

    if (kp != oldstate) {                  // Pressed key differs from previous

      cnt = 1;

      oldstate = kp;

      }

    else {                                 // Pressed key is same as previous

      cnt++;

      }

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

    if (cnt == 255) {                      // If counter varialble overflow

      cnt = 0;

      Lcd_Out(2, 10, "   ");

      }

    WordToStr(cnt, txt);                   // Transform counter value to string

    Lcd_Out(2, 10, txt);                   // Display counter value on Lcd

  } while (1);

}

HW Connection