interface 16x2 lcd with 8051

It is very important to keep a track of the working of almost all the automated and semi-automated devices, be it a washing machine, an autonomous robot or anything else. This is achieved by displaying their status on a small display module. LCD (Liquid Crystal Display) screen is such a display module and a 16x2 LCD module is very commonly used. These modules are replacing seven segments and other multi segment LEDs for these purposes. The reasons being: LCDs are economical, easily programmable, have no limitation of displaying special & even custom characters (unlike in seven segments), animationsand so on. LCD can be easily interfaced with a microcontroller to display a message or status of a device. This topic explains the basics of a 16x2 LCD and how it can be interfaced with AT89C51 to display a character.

A 16x2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5x7 pixel matrix. This LCD has two registers.

1.      Command/Instruction Register - stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing, clearing the screen, setting the cursor position, controlling display etc.

2.      Data Register - stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.

Commonly used LCD Command codes:

Hex Code	Command to LCD Instruction Register
1	Clear screen display
2	Return home
4	Decrement cursor
6	Increment cursor
E	Display ON, Cursor ON
80	Force the cursor to the beginning of the 1st line
C0	Force cursor to the beginning of the 2nd line
38	Use 2 lines and 5x7 matrix

Pin configuration:

Pin	Symbol	Description
1	VSS	Ground	0 V
2	VCC	Main power supply	+5 V
3	VEE	Power supply to control contrast	Contrast adjustment by providing a variable resistor through VCC
4	RS	Register Select	RS=0 to select Command Register RS=1 to select Data Register
5	R/W	Read/write	R/W=0 to write to the register R/W=1 to read from the register
6	EN	Enable	A high to low pulse (minimum 450ns wide) is given when data is sent to data pins
7	DB0	To display letters or numbers, their ASCII codes are sent to data pins (with RS=1). Also instruction command codes are sent to these pins.
8	DB1
9	DB2
10	DB3		8-bit data pins
11	DB4
12	DB5
13	DB6
14	DB7
15	Led+	Backlight VCC	+5 V
16	Led-	Backlight Ground	0 V

Programming the LCD:

 1.      Data pin8 (DB7) of the LCD is busy flag and is read when R/W = 1 & RS = 0. When busy flag=1, it means that LCD is not ready to accept data since it is busy with the internal operations. Therefore before passing any data to LCD, its command register should be read and busy flag should be checked.

2.      To send data on the LCD, data is first written to the data pins with R/W = 0 (to specify the write operation) and RS = 1 (to select the data register). A high to low pulse is given at EN pin when data is sent. Each write operation is performed on the positive edge of the Enable signal.

 3.      To send a command on the LCD, a particular command is first specified to the data pins with R/W = 0 (to specify the write operation) and RS = 0 (to select the command register). A high to low pulse is given at EN pin when data is sent.

Displaying single character ‘A’ on LCD

The LCD is interfaced with microcontroller (AT89C51). This microcontroller has 40 pins with four 8-bit ports (P₀, P₁, P₂, and P₃). Here P₁ is used as output port which is connected to data pins of the LCD. The control pins (pin 4-6) are controlled by pins 2-4 of P₀ port. Pin 3 is connected to a preset of 10k? to adjust the contrast on LCD screen. This program uses the above concepts of interfacing the LCD with controller by displaying the character ‘A’ on it.

code for lcd interface :

#include<reg51.h>
#define cmdport P3
#define dataport P2
#define q 100
sbit rs = cmdport^0;  //register select pin
sbit rw = cmdport^1;  // read write pin
sbit e = cmdport^6;  //enable pin

void delay(unsigned int msec)  // Function to provide time delay in msec.
{
int i,j ;
for(i=0;i<msec;i++)
for(j=0;j<1275;j++);
}

void lcdcmd(unsigned char item)  //Function to send command to LCD
{
dataport = item;
rs= 0;
rw=0;
e=1;
delay(1);
e=0;
}

void lcddata(unsigned char item)  //Function to send data to LCD
{
dataport = item;
rs= 1;
rw=0;
e=1;
delay(1);
e=0;
}

void main()
{
lcdcmd(0x38);  // for using 8-bit 2 row mode of LCD
delay(100);
lcdcmd(0x0E);  // turn display ON for cursor blinking
delay(100);
lcdcmd(0x01);  //clear screen
delay(100);
lcdcmd(0x06);  //display ON
delay(100);
lcdcmd(0x86);  // bring cursor to position 6 of line 1
delay(100);
lcddata('A');
}