Programming LCD in 4 bit and 8 bit mode using 8051

This type of LCD module is very common and used widely in many types of display applications. It consists of 16 rows and 2 columns of 5×7 dot matrices. The LCD display was a 16 pin package with back light, contrast adjustment and 5×7 dot resolution. It consists of two built in registers known as Data and Command register each has a specific function to perform. The Data register is for writing the data to be displayed and Command register is to write the commands. The pin description of 16×2 LCD was given below.
The Data and the Command both are fed to the LCD through the data pins D0 to D7 but the logic state in the RS pin decides whether it is data or command given to LCD. For sending commands the RS pin should be Logic 0 and for the data the RS Pin should be in Logic 1 or high state. After holding logic 0 or logic 1 at RS pin the microcontroller should wait for specific time for LCD to process it before sending the next command or data. 

The commands to the LCD was given in order to initialize the LCD and to give the starting address or position of the characters to be written in the LCD. The various commands to the LCD is given below.The above commands perform the function specified to them and should be given to the LCD with the Register select (RS) pin in logic 0.

MODE OF OPERATION:

1. 8 Bit mode.
2. 4 Bit mode.

DATA/COMMAND TRANSMISSION TO THE LCD:

The data transmission to a LCD must be performed by means of assigning logic states to three pins RS and E. R/W pin is not needed so we can ground it as shown in the schematic diagram. The data is send to the module by following these steps.

• RS pin should be high for a data transmission and low for a command transmission.
• Place the data/command in the data lines D0-D7 of the LCD.
• Pulse EN pin from high to low with certain time delay for transmission to complete.

Now lets move into the Programming of the LCD using this AT89S52 microcontroller and this programming was done by using Keil Uvision Software.

#include<reg51.h> 
#define LCD P2
sbit RS=P3^0; 
sbit EN=P3^1; 
unsigned char txt[12]="GADGETRONICX";       //Data to display
void delay()  
 {   
   int k;   
   for(k=0;k<=1000;k++); 
  } 
void lcd(char a,short int b)       //Subroutine for command and data transmission 
  {   
   LCD=a;                             //Placing byte in D0-D7 lines of LCD
   RS=b;                              //0 for command and 1 for data
   EN=1;   
   delay();   
   EN=0; 
  }
void main()
{
   int i=0;
   lcd(0x38,0);                      //Initializing LCD
   lcd(0x0f,0);   
   lcd(0x01,0);  
   lcd(0x02,0); 
   lcd(0x80,0);   
   for(i=0;i<=11;i++)           //Transmitting Data
    {
      lcd(txt[i],1);
    }
   while(1);
 }

In 8 bit mode LCD requires uses 4 pins for data/command transmission from the microcontroller. The data/ command bytes will be sent through the pins (D4-D7) higher bits along with EN,RS and RW(optional) of the LCD. So we need to dedicate a total of 7 pins from the Microcontroller to the LCD.  

The main difference between the 4 and 8 bit mode is usage of pins from the microcontroller. Also 8 bit mode is faster than the four bit mode which sends the data in the form of nibbles (4 bits).

DESIGN:

#include<reg51.h>
#define LCD     P2
#define ENABLE      0x10
#define REG_SL      0x20

void delay()
 {
   int i,j;
   for(i=0;i<=500;i++);
   for(j=0;j<=500;j++);
 }

void lcd_reset()                   //Reset sequence as stated in the LCD datasheet
 {
LCD = 0xFF;
delay();
LCD = 0x03|ENABLE;
LCD = 0x03;
delay();
LCD = 0x03|ENABLE;
LCD = 0x03;
delay();
LCD = 0x03|ENABLE;
LCD = 0x03;
delay();
LCD = 0x02|ENABLE;
LCD = 0x02;
delay();
 }

void lcd_cmd(char cmd)               //Subroutine to send command
 { 
LCD = ((cmd>>4)&0x0F)|ENABLE;     //Sending higher nibble by shifting with Pulsing Enable high
delay();
LCD = ((cmd>>4)&0x0F);
  delay();
LCD = (cmd & 0x0F)|ENABLE;          //Sending lower nibble Enable low
LCD = (cmd & 0x0F);
 }

void lcd_data (char *dat)          //Subroutine to send data
 { 
  while(*dat!='')
{
LCD = (((*dat>>4)&0x0F)|ENABLE|REG_SL); //Sending data by making RS=1
delay();
LCD = (((*dat>>4)&0x0F)|REG_SL);
delay();
LCD = ((*dat & 0x0F)|ENABLE|REG_SL);
delay();
LCD = ((*dat & 0x0F)|REG_SL);
delay();
dat++;
}
 }

void lcd_init ()
 {
lcd_cmd(0x28);       // 4-bit mode - 2 line - 5x7 font. 
lcd_cmd(0x0F);       // Display cursor with blink.
lcd_cmd(0x06);       // Automatic Increment - No Display shift.
   lcd_cmd(0x01);
   lcd_cmd(0x02);       //Clear screen and return home    
lcd_cmd(0x80);       // First row first column
  }

 void main()
  {
    lcd_reset();
    lcd_init();
    lcd_data("GADGETRONICX");
    while(1);
  }