LCD 4-BIT MODE with 8051

LCD 4-BIT MODE with 8051

TO know the Basic of LCD go to the previous post click here .
There are many reasons why sometime we prefer to use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

In 4-bit mode the data is sent in nibbles, first we send the higher nibble and then the lower nibble. To enable the 4-bit mode of LCD, we need to follow special sequence of initialization that tells the LCD controller that user has selected 4-bit mode of operation. We call this special sequence as resetting the LCD. Following is the reset sequence of LCD.
  • Wait for abour 20mS
  • Send the first init value (0x30)
  • Wait for about 10mS
  • Send second init value (0x30)
  • Wait for about 1mS
  • Send third init value (0x30)
  • Wait for 1mS
  • Select bus width(0x30 - for 8-bit and 0x20 for 4-bit)
  • Wait for 1mS

The busy flag will only be valid after the above reset sequence. Usually we do not use busy flag in 4-bit mode as we have to write code for reading two nibbles from the LCD. Instead we simply put a certain ammount of delay usually 300 to 600uS. This delay might vary depending on the LCD you are using, as you might have a different crystal frequency on which LCD controller is running. So it actually depends on the LCD MODULE you are using. So if you feel any problem running the LCD, simply try to increase the delay. This usually works. For me about 400uS works perfect.
LCD connections in 4-bit Mode




Above is the connection diagram of LCD in 4-bit mode, where we only need 6 pins to interface an LCD. D4-D7 are the data pins connection and Enable and Register select are for LCD control pins. We are not using Read/Write (RW) Pin of the LCD, as we are only writing on the LCD so we have made it grounded permanently. If you want to use it.. then you may connect it on your controller but that will only increase another pin and does not make any big difference. Potentiometer RV1 is used to control the LCD contrast. The unwanted data pins of LCD i.e. D0-D3 are connected to ground.
LCD connections in 4-bit Mode
We will now look into the common steps to send data/command to LCD when working in 4-bit mode. As i already explained in 4-bit mode data is sent nibble by nibble, first we send higher nibble and then lower nibble. This means in both command and data sending function we need to saperate the higher 4-bits and lower 4-bits.


The common steps are:
  • Mask lower 4-bits
  • Send to the LCD port
  • Send enable signal
  • Mask higher 4-bits
  • Send to LCD port
  • Send enable signal
Program
 lcd.c file 

#include<reg51.h>

#include<stdio.h>   

#define LCDPORT P2

sbit RS = LCDPORT ^ 0;
sbit RW = LCDPORT ^ 1;
sbit E = LCDPORT ^ 2;
#include "lcd.h"     
void main()
{
lcd_init();
lcd_com(15);
lcd_puts("test");
lcd_com(0XC0);
lcd_puts("World");
while (1);
}

  ---------------------------------------------------------------------------------------------------------------------------


lcd.h file .




bit status = 0;
#define lcd_delay 400 
void delay(unsigned int j)
{
    unsigned int i = 0;
    for (; i < j; i++);
} 
void _lcd_init_write(unsigned char a)
{
    RS = 0;
    RW = 0;
    LCDPORT = a;
    E = 1;
    delay(lcd_delay);
    E = 0;
} 
void lcd_com(unsigned char a)
{
    unsigned char temp;
    if (status) {
     status = 0;
     goto next;
    }
    RS = 0;
  next:
  RW = 0;
    temp = a;
    temp &= 0xf0;
    LCDPORT &= 0x0f;
    LCDPORT |= temp;
    E = 1;
    delay(lcd_delay);
    E = 0;
    temp = a << 4;
    temp &= 0xf0;
    LCDPORT &= 0x0f;
    LCDPORT |= temp;
    E = 1;
    delay(lcd_delay);
    E = 0;
}

void lcd_data(unsigned char a)
{
    status = 1;
    RS = 1;
    lcd_com(a);
}



void lcd_init(void)
{
    delay(lcd_delay);
    lcd_init_write(0x30);
    delay(lcd_delay);
    lcd_init_write(0x30);
    delay(lcd_delay);
    lcd_init_write(0x30);
    delay(lcd_delay);
    lcd_init_write(0x20);
    delay(lcd_delay);
    lcd_com(0x28);
    delay(lcd_delay);
    lcd_com(4);
    delay(lcd_delay);
    lcd_com(0x85);
    delay(lcd_delay);
    lcd_com(6);
    delay(lcd_delay);
    lcd_com(1);
    delay(lcd_delay);
}


void lcd_puts(char *aaa)
{
    unsigned int i = 0;
    for (; aaa[i] != 0; i++)
     lcd_data(aaa[i]);
}

Download here the Proteus and Keil File Click Here






 
 
Till now whatever we discussed in the previous part of ths LCD tutorial, we were dealing with 8-bit mode. Now we are going to learn how to use LCD in 4-bit mode. There are many reasons why sometime we prefer to use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

In 4-bit mode the data is sent in nibbles, first we send the higher nibble and then the lower nibble. To enable the 4-bit mode of LCD, we need to follow special sequence of initialization that tells the LCD controller that user has selected 4-bit mode of operation. We call this special sequence as resetting the LCD. Following is the reset sequence of LCD.
  1. Wait for abour 20mS
  2. Send the first init value (0x30)
  3. Wait for about 10mS
  4. Send second init value (0x30)
  5. Wait for about 1mS
  6. Send third init value (0x30)
  7. Wait for 1mS
  8. Select bus width (0x30 - for 8-bit and 0x20 for 4-bit)
  9. Wait for 1mS
- See more at: http://www.8051projects.net/lcd-interfacing/lcd-4-bit.php#sthash.MwfMgDYA.dpuf
Till now whatever we discussed in the previous part of ths LCD tutorial, we were dealing with 8-bit mode. Now we are going to learn how to use LCD in 4-bit mode. There are many reasons why sometime we prefer to use LCD in 4-bit mode instead of 8-bit. One basic reason is lesser number of pins are needed to interface LCD.

In 4-bit mode the data is sent in nibbles, first we send the higher nibble and then the lower nibble. To enable the 4-bit mode of LCD, we need to follow special sequence of initialization that tells the LCD controller that user has selected 4-bit mode of operation. We call this special sequence as resetting the LCD. Following is the reset sequence of LCD.
  1. Wait for abour 20mS
  2. Send the first init value (0x30)
  3. Wait for about 10mS
  4. Send second init value (0x30)
  5. Wait for about 1mS
  6. Send third init value (0x30)
  7. Wait for 1mS
  8. Select bus width (0x30 - for 8-bit and 0x20 for 4-bit)
  9. Wait for 1mS
- See more at: http://www.8051projects.net/lcd-interfacing/lcd-4-bit.php#sthash.MwfMgDYA.dpuf

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