Overview of LCD16x2

LCDs (Liquid Crystal Displays) are used for displaying status or parameters in embedded systems.

LCD 16x2 is a 16 pin device which has 8 data pins (D0-D7) and 3 control pins (RS, RW, EN). The remaining 5 pins are for supply and backlight for the LCD.

The control pins help us configure the LCD in command mode or data mode. They also help configure read mode or write mode and also when to read or write.

LCD 16x2 can be used in 4-bit mode or 8-bit mode depending on the requirement of the application. In order to use it, we need to send certain commands to the LCD in command mode and once the LCD is configured according to our need, we can send the required data in data mode.

For more information about LCD 16x2 and how to use it, refer to the topic LCD 16x2 display module in the sensors and modules section.

LCD16x2 Pinout

LCD16x2 4-bit Mode 

• In 4-bit mode, data/command is sent in a 4-bit (nibble) format.
• To do this 1st send a Higher 4-bit and then send a lower 4-bit of data/command.
• Only 4 data (D4 - D7) pins of 16x2 of LCD are connected to the microcontroller and other control pins RS (Register select), RW (Read/write), E (Enable) is connected to other GPIO Pins of the controller.

Therefore, due to such connections, we can save four GPIO pins which can be used for another application.

Connection Diagram of LCD16x2 with ATmega16/32

Programming LCD16x2 4-bit mode with AVR ATmega16/Atmega32

Initialization

1. Wait for 15ms, Power-on initialization time for LCD16x2.
2. Send 0x02 command which initializes LCD 16x2 in 4-bit mode.
3. Send 0x28 command which configures LCD in 2-line, 4-bit mode, and 5x8 dots.
4. Send any Display ON command (0x0E, 0x0C)
5. Send 0x06 command (increment cursor)

void LCD_Init (void)  /* LCD Initialize function */
{
	LCD_Dir = 0xFF;		/* Make LCD port direction as o/p */
	_delay_ms(20);		/* LCD Power ON delay always >15ms */
	
	LCD_Command(0x33);
	LCD_Command(0x32);	/* Send for 4 bit initialization of LCD  */
	LCD_Command(0x28);	/* 2 line, 5*7 matrix in 4-bit mode */
	LCD_Command(0x0c);	/* Display on cursor off */
	LCD_Command(0x06);	/* Increment cursor (shift cursor to right) */
	LCD_Command(0x01);	/* Clear display screen */
}

Now we successfully initialized LCD & it is ready to accept data in 4-bit mode to display.

To send command/data to 16x2 LCD we have to send higher nibble followed by lower nibble. As 16x2 LCD’s D4 - D7 pins are connected as data pins, we have to shift the lower nibble to the right by 4 before transmitting.

Command write function

1. First, send a Higher nibble of command.
2. Make RS pin low, RS=0 (command reg.)
3. Make RW pin low, RW=0 (write operation) or connect it to ground.
4. Give High to Low pulse at Enable (E).
5. Send lower nibble of command.
6. Give High to Low pulse at Enable (E).

void LCD_Command( unsigned char cmnd )
{
	LCD_Port = (LCD_Port & 0x0F) | (cmnd & 0xF0);/* Sending upper nibble */
	LCD_Port &= ~ (1<<RS);		/* RS=0, command reg. */
	LCD_Port |= (1<<EN);		/* Enable pulse */
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_us(200);
	LCD_Port = (LCD_Port & 0x0F) | (cmnd << 4);/* Sending lower nibble */
	LCD_Port |= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_ms(2);
}

Data write function

1. First, send a Higher nibble of data.
2. Make RS pin high, RS=1 (data reg.)
3. Make RW pin low, RW=0 (write operation) or connect it to ground.
4. Give High to Low pulse at Enable (E).
5. Send lower nibble of data.
6. Give High to Low pulse at Enable (E).

void LCD_Char( unsigned char data )
{
	LCD_Port = (LCD_Port & 0x0F) | (data & 0xF0);/* Sending upper nibble */
	LCD_Port |= (1<<RS);  /* RS=1, data reg. */
	LCD_Port|= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_us(200);
	LCD_Port = (LCD_Port & 0x0F) | (data << 4);  /* Sending lower nibble */
	LCD_Port |= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_ms(2);
}

LCD16x2 4 bit Mode Code for ATmega16/32

/*  
   LCD16x2 4 bit ATmega16 interface
   http://www.electronicwings.com
*/

#define F_CPU 8000000UL			/* Define CPU Frequency e.g. here 8MHz */
#include <avr/io.h>			/* Include AVR std. library file */
#include <util/delay.h>			/* Include Delay header file */

#define LCD_Dir  DDRB			/* Define LCD data port direction */
#define LCD_Port PORTB			/* Define LCD data port */
#define RS PB0				/* Define Register Select pin */
#define EN PB1 				/* Define Enable signal pin */

void LCD_Command( unsigned char cmnd )
{
	LCD_Port = (LCD_Port & 0x0F) | (cmnd & 0xF0); /* sending upper nibble */
	LCD_Port &= ~ (1<<RS);		/* RS=0, command reg. */
	LCD_Port |= (1<<EN);		/* Enable pulse */
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);

	_delay_us(200);

	LCD_Port = (LCD_Port & 0x0F) | (cmnd << 4);  /* sending lower nibble */
	LCD_Port |= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_ms(2);
}

void LCD_Char( unsigned char data )
{
	LCD_Port = (LCD_Port & 0x0F) | (data & 0xF0); /* sending upper nibble */
	LCD_Port |= (1<<RS);		/* RS=1, data reg. */
	LCD_Port|= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);

	_delay_us(200);

	LCD_Port = (LCD_Port & 0x0F) | (data << 4); /* sending lower nibble */
	LCD_Port |= (1<<EN);
	_delay_us(1);
	LCD_Port &= ~ (1<<EN);
	_delay_ms(2);
}

void LCD_Init (void)			/* LCD Initialize function */
{
	LCD_Dir = 0xFF;			/* Make LCD port direction as o/p */
	_delay_ms(20);			/* LCD Power ON delay always >15ms */
	
	LCD_Command(0x02);		/* send for 4 bit initialization of LCD  */
	LCD_Command(0x28);              /* 2 line, 5*7 matrix in 4-bit mode */
	LCD_Command(0x0c);              /* Display on cursor off*/
	LCD_Command(0x06);              /* Increment cursor (shift cursor to right)*/
	LCD_Command(0x01);              /* Clear display screen*/
	_delay_ms(2);
}

void LCD_String (char *str)		/* Send string to LCD function */
{
	int i;
	for(i=0;str[i]!=0;i++)		/* Send each char of string till the NULL */
	{
		LCD_Char (str[i]);
	}
}

void LCD_String_xy (char row, char pos, char *str)	/* Send string to LCD with xy position */
{
	if (row == 0 && pos<16)
	LCD_Command((pos & 0x0F)|0x80);	/* Command of first row and required position<16 */
	else if (row == 1 && pos<16)
	LCD_Command((pos & 0x0F)|0xC0);	/* Command of first row and required position<16 */
	LCD_String(str);		/* Call LCD string function */
}

void LCD_Clear()
{
	LCD_Command (0x01);		/* Clear display */
	_delay_ms(2);
	LCD_Command (0x80);		/* Cursor at home position */
}
 
int main()
{
	LCD_Init();			/* Initialization of LCD*/

	LCD_String("ElectronicWINGS");	/* Write string on 1st line of LCD*/
	LCD_Command(0xC0);		/* Go to 2nd line*/
	LCD_String("Hello World");	/* Write string on 2nd line*/
	while(1);
}