Interfacing LCD with PIC Microcontroller – MPLAB XC8

Interfacing LCD with PIC Microcontroller – MPLAB XC8

In this tutorial we will see How to Interface a 16×2 character LCD module with PIC 16F877A Microcontroller using MPLAB X IDE and MPLAB XC8 C Compiler. 16×2 Character LCD is a very basic and low cost LCD module which is commonly used in electronic products and projects. 16×2 means it contains 2 rows that can display 16 characters. Its other variants such as 16×1 and 16×4 are also available in the market. In these displays, each character is displayed using 5×8 or 5×10 dot matrix.

For controlling LCD using MPLAB XC8 compiler we need to know the hardware of LCD. These LCDs commonly uses HD44780 compliant controllers. So we need to learn HD44780 Dot Matrix LCD Controller Datasheet. Don’t worry we already developed an LCD library including commonly used functions, so you can use it without any hardware knowledge of LCD.

16x2 LCD Pin Diagram

16×2 LCD Pin Diagram

First two pins GND and VCC (VSS and VDD) are for providing power to LCD display. 3ed pin VEE is used to control the contrast of the LCD display. A 10KΩ preset whose fixed ends connected to VDD, VSS and variable end connected to VEE can be used to control contrast of the LCD. A microcontroller or microprocessor need to send 2 types of information for operating this LCD Module, Data Information and Command Information. Data Information is the ASCII value of the characters to be displayed in the LCD screen and Command Information determines other operations such as position to be displayed, clear screen, shift etc. Data and Command Information are send to LCD through same data lines (DB0 – DB7) which are multiplexed using RS (Register Select) pin of LCD. When RS is HIGH LCD treats DB0 – DB7 data pins information as Data to be displayed and when it is LOW LCD treats it as Command Information. Enable (E) input of the LCD is used to give Data Strobe. HIGH (5V) Voltage Level in the Enable (E) pin tells the LCD that DB0 – DB7 contains valid information. The input signal R/W (Read or Write) determines whether data is written to or read from the LCD. In normal cases we need only writing hence it is tied to GROUND in circuit shown below.

The interface between this LCD and Microcontroller can be 8 bit or 4 bit and the difference between them is in how the data or commands are send to LCD. In the 8 bit mode, 8 bit data and commands are send through the data lines DB0 – DB7 and data strobe is given through E input of the LCD. But 4 bit mode uses only 4 data lines. In this 8 bit data and commands are splitted into 2 parts (4 bits each) and are sent sequentially through data lines DB4 – DB7 with its own data strobe through E input. The idea of 4 bit communication is introduced to save pins of a microcontroller. You may think that 4 bit mode will be slower than 8 bit. But the speed difference is only minimal. As LCDs are slow speed devices, the tiny speed difference between these modes is not significant. Just remember that microcontroller is operating at high speed in the range of MHz and we are viewing LCD with our eyes. Due to Persistence of Vision of our eyes we will not even feel the speed difference.


Hope that you got rough idea about how this LCD Module works. Actually you need to read the datasheet of HD44780 LCD driver used in this LCD Module to write a MPLAB XC8 program for PIC. But we solved this problem by creating a header file lcd.h which includes all the commonly used functions using 4 bit mode. Just include it and enjoy.

Circuit Diagram

Interfacing LCD with PIC Microcontroller - Circuit Diagram

Interfacing LCD with PIC Microcontroller – Circuit Diagram

LCD Library

  • Lcd_Init() : This function will initialize the LCD Module connected to the following defined pins.
#define RS RD2
#define EN RD3
#define D4 RD4
#define D5 RD5
#define D6 RD6
#define D7 RD7

These connections must be defined for the proper working of LCD.

  • Lcd_Clear() : To clear the display.
  • Lcd_Set_Cursor(int row, int column) : This function is used to set row and column of the cursor on the LCD screen. By using this function we can change the position of the character or string displayed by following functions.
  • Lcd_Write_Char(char) : To write a character to LCD on the current position.
  • Lcd_Write_String(char *string) : To write string to LCD on the current position.
  • Lcd_Shift_Right() : To shift contents on the LCD screen Right once without changing the data in the Display RAM.
  • Lcd_Shift_Left() : To shift contents on the LCD screen Left once without changing the data in the Display RAM.

Note : The Pins to which LCD is connecting should be configured as Output Pins by writing to TRIS Register.

MPLAB XC8 Code

#define _XTAL_FREQ 8000000

#define RS RD2
#define EN RD3
#define D4 RD4
#define D5 RD5
#define D6 RD6
#define D7 RD7

#include <xc.h>
#include "lcd.h";

// BEGIN CONFIG
#pragma config FOSC = HS // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT enabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = OFF // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
#pragma config CPD = OFF // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF // Flash Program Memory Code Protection bit (Code protection off)
//END CONFIG

int main()
{
    unsigned int a;
    TRISD = 0x00;
    Lcd_Init();
    while(1)
    {
        Lcd_Clear();
        Lcd_Set_Cursor(1,1);
        Lcd_Write_String("LCD Library for");
        Lcd_Set_Cursor(2,1);
        Lcd_Write_String("MPLAB XC8");
        __delay_ms(2000);
        Lcd_Clear();
        Lcd_Set_Cursor(1,1);
        Lcd_Write_String("Developed By");
        Lcd_Set_Cursor(2,1);
        Lcd_Write_String("electroSome");
        __delay_ms(2000);
        Lcd_Clear();
        Lcd_Set_Cursor(1,1);
        Lcd_Write_String("www.electroSome.com");

        for(a=0;a<15;a++)
        {
            __delay_ms(300);
            Lcd_Shift_Left();
        }

        for(a=0;a<15;a++)
        {
            __delay_ms(300);
            Lcd_Shift_Right();
        }

        Lcd_Clear();
        Lcd_Set_Cursor(2,1);
        Lcd_Write_Char('e');
        Lcd_Write_Char('S');
        __delay_ms(2000);
    }
    return 0;
}

sprintf() to Format Outputs

sprintf() can be used to write formatted string to a variable. It can be used with this LCD library to format displayed texts. This enables us to display integers and floating point numbers on the LCD very easily.

Syntax :

sprintf(char * str, const char * format, ...);

Where,

  • str is the pointer to the buffer to which the resulting string is to be stored.
  • format is a constant string or null terminated array of characters. Formatting is done in accordance with this argument.
  • … (additional arguments) indicate a list of additional arguments that may required for this function depending up on the format string. Each additional argument contains a value that to be replace a format specifier in the format string.

Format Specifiers

The generic form of format is %nt. where n is optional which may be 1 – 9 to specify number of characters to be outputted or 01 – 09 to indicate leading zeros or 1.1 to 9.9 for floating point and %w formats. t is the type which may be one of the following.

tType
cCharacter
sSting or Character
uUnsigned Integer
dSigned Integer
LuLong Unsigned Integer
LdLong Signed Integer
xHex Integer – lower case
XHex Integer – upper case
LxHex Long Integer – lower case
LXHex Long Integer – upper case
fFloat with truncated decimal
gFloat with rounded decimal
eFloat in exponential format
wUnsigned Integer with decimal place inserted. Specify two numbers for n. The first is a total field width. The second is the desired number of decimal places.

 Example :

....
float f = 1.414;
int a = 56;
char s[20];
....
....
sprintf(s, "Float = %f", f);
Lcd_Set_Cursor(1,1);
Lcd_Write_String(s);
sprintf(s, "Integer = %d", a);
Lcd_Set_Cursor(2,1);
Lcd_Write_String(s);

This code will make following output on the LCD.

Display Integer and Floating Point Number on LCD

Display Integer and Floating Point Number on LCD

Please go to this page for more details about formatting.

Download Here

If you have and doubts, just comment below. You can download the entire project files here…

Want to See the Output ?


 

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