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AVR 4 Bit LCD Interfacing Tutorial


The mikroC PRO for AVR provides a library for communication with Lcds (with HD44780 compliant controllers) through the 4-bit interface. An example of Lcd connections is given on the schematic at the bottom of this page.

For LCD Basics: Character LCD Basics 


Lcd Library



External dependencies of Lcd Library
The following variables must be defined in all projects using Lcd Library :
Description :
Example :
extern sfr sbit LCD_RS:
Register Select line.
sbit LCD_RS at PORTD2_bit;
extern sfr sbit LCD_EN:
Enable line.
sbit LCD_EN at PORTD3_bit;
extern sfr sbit LCD_D7;
Data 7 line.
sbit LCD_D7 at PORTD4_bit;
extern sfr sbit LCD_D6;
Data 6 line.
sbit LCD_D6 at PORTD5_bit;
extern sfr sbit LCD_D5;
Data 5 line.
sbit LCD_D5 at PORTD6_bit;
extern sfr sbit LCD_D4;
Data 4 line.
sbit LCD_D4 at PORTD7_bit;
extern sfr sbit LCD_RS_Direction;
Register Select direction pin.
sbit LCD_RS_Direction at DDD2_bit;
extern sfr sbit LCD_EN_Direction;
Enable direction pin.
sbit LCD_EN_Direction at DDD3_bit;
extern sfr sbit LCD_D7_Direction;
Data 7 direction pin.
sbit LCD_D7_Direction at DDD4_bit;
extern sfr sbit LCD_D6_Direction;
Data 6 direction pin.
sbit LCD_D6_Direction at DDD5_bit;
extern sfr sbit LCD_D5_Direction;
Data 5 direction pin.
sbit LCD_D5_Direction at DDD6_bit;
extern sfr sbit LCD_D4_Direction;
Data 4 direction pin.
sbit LCD_D4_Direction at DDD7_bit;
Library Routines
Lcd_Init
Prototype
void Lcd_Init();
Returns
Nothing.
Description
Initializes Lcd module.
Requires
Global variables:
  • LCD_D7: Data bit 7
  • LCD_D6: Data bit 6
  • LCD_D5: Data bit 5
  • LCD_D4: Data bit 4
  • LCD_RS: Register Select (data/instruction) signal pin
  • LCD_EN: Enable signal pin
  • LCD_D7_Direction: Direction of the Data 7 pin
  • LCD_D6_Direction: Direction of the Data 6 pin
  • LCD_D5_Direction: Direction of the Data 5 pin
  • LCD_D4_Direction: Direction of the Data 4 pin
  • LCD_RS_Direction: Direction of the Register Select pin
  • LCD_EN_Direction: Direction of the Enable signal pin
must be defined before using this function.
Example
// Lcd pinout settings
sbit LCD_RS at PORTD2_bit;
sbit LCD_EN at PORTD3_bit;
sbit LCD_D7 at PORTD4_bit;
sbit LCD_D6 at PORTD5_bit;
sbit LCD_D5 at PORTD6_bit;
sbit LCD_D4 at PORTD7_bit;

// Pin direction
sbit LCD_RS_Direction at DDD2_bit;
sbit LCD_EN_Direction at DDD3_bit;
sbit LCD_D7_Direction at DDD4_bit;
sbit LCD_D6_Direction at DDD5_bit;
sbit LCD_D5_Direction at DDD6_bit;
sbit LCD_D4_Direction at DDD7_bit;
...

Lcd_Init();
Lcd_Out
Prototype
void Lcd_Out(char row, char column, char *text);
Returns
Nothing.
Description
Prints text on Lcd starting from specified position. Both string variables and literals can be passed as a text.
Parameters :
  • row: starting position row number
  • column: starting position column number
  • text: text to be written
Requires
The Lcd module needs to be initialized. See Lcd_Init routine.
Example
// Write text "Hello!" on Lcd starting from row 1, column 3:
Lcd_Out(1, 3, "Hello!");
Lcd_Out_Cp
Prototype
void Lcd_Out_Cp(char *text);
Returns
Nothing.
Description
Prints text on Lcd at current cursor position. Both string variables and literals can be passed as a text.
Parameters :
  • text: text to be written
Requires
The Lcd module needs to be initialized. See Lcd_Init routine.
Example
// Write text "Here!" at current cursor position:
Lcd_Out_Cp("Here!");
Lcd_Chr
Prototype
void Lcd_Chr(char row, char column, char out_char);
Returns
Nothing.
Description
Prints character on Lcd at specified position. Both variables and literals can be passed as a character.
Parameters :
  • row: writing position row number
  • column: writing position column number
  • out_char: character to be written
Requires
The Lcd module needs to be initialized. See Lcd_Init routine.
Example
// Write character "i" at row 2, column 3:
Lcd_Chr(2, 3, 'i');
Lcd_Chr_Cp
Prototype
void Lcd_Chr_Cp(char out_char);
Returns
Nothing.
Description
Prints character on Lcd at current cursor position. Both variables and literals can be passed as a character.
Parameters :
  • out_char: character to be written
Requires
The Lcd module needs to be initialized. See Lcd_Init routine.
Example
// Write character "e" at current cursor position:
Lcd_Chr_Cp('e');
Lcd_Cmd
Prototype
void Lcd_Cmd(char out_char);
Returns
Nothing.
Description
Sends command to Lcd.
Parameters :
  • out_char: command to be sent
  Note : Predefined constants can be passed to the function, see Available Lcd Commands.
Requires
The Lcd module needs to be initialized. See Lcd_Init table.
Example
// Clear Lcd display:
Lcd_Cmd(_LCD_CLEAR);
Available Lcd Commands
Lcd Command
Purpose
_LCD_FIRST_ROW
Move cursor to the 1st row
_LCD_SECOND_ROW
Move cursor to the 2nd row
_LCD_THIRD_ROW
Move cursor to the 3rd row
_LCD_FOURTH_ROW
Move cursor to the 4th row
_LCD_CLEAR
Clear display
_LCD_RETURN_HOME
Return cursor to home position, returns a shifted display to its original position. Display data RAM is unaffected.
_LCD_CURSOR_OFF
Turn off cursor
_LCD_UNDERLINE_ON
Underline cursor on
_LCD_BLINK_CURSOR_ON
Blink cursor on
_LCD_MOVE_CURSOR_LEFT
Move cursor left without changing display data RAM
_LCD_MOVE_CURSOR_RIGHT
Move cursor right without changing display data RAM
_LCD_TURN_ON
Turn Lcd display on
_LCD_TURN_OFF
Turn Lcd display off
_LCD_SHIFT_LEFT
Shift display left without changing display data RAM
_LCD_SHIFT_RIGHT
Shift display right without changing display data RAM
Example
The following code demonstrates usage of the Lcd Library routines:
           // LCD module connections
sbit LCD_RS at PORTD2_bit;
sbit LCD_EN at PORTD3_bit;
sbit LCD_D4 at PORTD4_bit;
sbit LCD_D5 at PORTD5_bit;
sbit LCD_D6 at PORTD6_bit;
sbit LCD_D7 at PORTD7_bit;

sbit LCD_RS_Direction at DDD2_bit;
sbit LCD_EN_Direction at DDD3_bit;
sbit LCD_D4_Direction at DDD4_bit;
sbit LCD_D5_Direction at DDD5_bit;
sbit LCD_D6_Direction at DDD6_bit;
sbit LCD_D7_Direction at DDD7_bit;
// End LCD module connections

char txt1[] = "Embedded";
char txt2[] = "Projects";
char txt3[] = "Lcd 4 bit";
char txt4[] = "Tutorial";

char i;                              // Loop variable

void Move_Delay() {                  // Function used for text moving
  Delay_ms(500);                     // You can change the moving speed here
}

void main(){
  Lcd_Init();                        // Initialize LCD
  Lcd_Cmd(_LCD_CLEAR);               // Clear display
  Lcd_Cmd(_LCD_CURSOR_OFF);          // Cursor off

  Lcd_Out(1,6,txt3);                 // Write text in first row
  Lcd_Out(2,6,txt4);                 // Write text in second row
  Delay_ms(2000);
  Lcd_Cmd(_LCD_CLEAR);               // Clear display

  Lcd_Out(1,1,txt1);                 // Write text in first row
  Lcd_Out(2,4,txt2);                 // Write text in second row
  Delay_ms(2000);

  // Moving text
  for(i=0; i<4; i++) {               // Move text to the right 4 times
    Lcd_Cmd(_LCD_SHIFT_RIGHT);
    Move_Delay();
  }

  while(1) {                         // Endless loop
    for(i=0; i<7; i++) {             // Move text to the left 7 times
      Lcd_Cmd(_LCD_SHIFT_LEFT);
      Move_Delay();
    }

    for(i=0; i<7; i++) {             // Move text to the right 7 times
      Lcd_Cmd(_LCD_SHIFT_RIGHT);
      Move_Delay();
    }

  }
}

Circuit diagram

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