LCD Interfacing with 8051 Microcontroller

The interfacing of a 16x2 LCD display with 8051 microcontroller is very popular and one of the most important in embedded systems programming. This tutorial will explain the complete LCD interfacing of 8051 C program, circuit connections, and coding strategies in a program with the use of the AT89S52 microcontroller.

The display units are the most important output devices in embedded projects and electronics products. The 16X2 LCD module is designed to display characters per line, which means in this case sixteen characters across two lines.  Each character occupies a 5x7 matrix space on display. Interfacing LCD with 8051 microcontroller is a little complicated at the beginning, but when one properly understands the 16-pin configuration and control signals, it becomes direct and easy to design for practical applications.

Understanding 16x2 LCD Display Module Pinout

Before interfacing LCD with 8051 diagram, there are some important things to note about the 16-pin configuration. In order to perform 16x2 LCD display interfacing with the 8051 microcontroller, we need to connect power pins, control pins, data pins, backlight pins etc.to complete the communication properly.

We can divide it into five categories: Power Pins, contrast pin, Control Pins, Data pins and Backlight pins.

Category	Pin NO.	Pin Name	Function
Power Pins	1	VSS	Ground Pin, connected to Ground
	2	VDD or Vcc	Voltage Pin +5V
Contrast Pin	3	V0 or VEE	Contrast Setting, connected to Vcc thorough a variable resistor.
Control Pins	4	RS	Register Select Pin, RS=0 Command mode, RS=1 Data mode
	5	RW	Read/ Write pin, RW=0 Write mode, RW=1 Read mode
	6	E	Enable, a high to low pulse need to enable the LCD
Data Pins	7-14	D0-D7	Data Pins, Stores the Data to be displayed on LCD or the command instructions
Backlight Pins	15	LED+ or A	To power the Backlight +5V
	16	LED- or K	Backlight Ground

Control Pins Detailed Explanation (RS, RW, E)

The control pins are a key component in interfacing LCD with 8051 microcontroller. Without learning how they work, the communication to the LCD will not be successful: 

All the pins are understandable by their name and functions, except the control pins, so they are explained below:

RS: RS is the register select pin. We need to set it to 1 if we are sending some data to be displayed on the LCD. And we will set it to 0 if we are sending some command instruction like clear the screen (hex code 01).

RW: This is a read/write pin; we will set it to 0 if we are going to write some data on the LCD. And set it to 1, if we are reading from the LCD module. Generally, this is set to 0, because we do not need to read data from the LCD. Only one instruction, “Get LCD status”, needs to be read some times. In most LCD interfacing with 8051 C program implementations, this pin is kept at 0 since reading from LCD is rarely required.

E: This pin is used to enable the module when a high-to-low pulse is given to it. A pulse of 450 ns should be given. That transition from HIGH to LOW makes the module ENABLE.

LCD Interfacing with 8051 Diagram and Hardware Setup

The circuit diagram for interfacing the LCD with 8051 shows all of the hardware connections needed to successfully connect the AT89S52 microcontroller and the 16x2 LCD module. Having your wiring right is important to ensure proper functionality.
 

There are some preset command instructions on the LCD. We have used them in our program below to prepare the LCD (in the lcd_init() function). Some important command instructions are given below:

Hex Code	Command to LCD Instruction Register
0F	LCD ON, cursor ON
01	Clear display screen
02	Return home
04	Decrement cursor (shift cursor to left)
06	Increment cursor (shift cursor to right)
05	Shift display right
07	Shift display left
0E	Display ON, cursor blinking
80	Force cursor to beginning of first line
C0	Force cursor to beginning of second line
38	2 lines and 5×7 matrix
83	Cursor line 1 position 3
3C	Activate second line
08	Display OFF, cursor OFF
C1	Jump to second line, position 1
OC	Display ON, cursor OFF
C1	Jump to second line, position 1
C2	Jump to second line, position 2

 

LCD Interfacing with 8051 Diagram and Explanation

The circuit diagram for LCD interfacing with 8051 microcontroller is shown in the above figure. If you have a basic understanding of 8051, then you must know about EA(PIN 31), XTAL1 & XTAL2, RST pin(PIN 9), Vcc and Ground Pin of the 8051 microcontroller. I have used these Pins in the above circuit. If you don’t have any idea about that, then I recommend that you read this Article, LED Interfacing with 8051 Microcontroller, before going through LCD interfacing.

Hardware Connections and Wiring Guide

So besides these above pins, we have connected the data pins (D0-D7) of the LCD to the Port 2 (P2_0–P2_7) microcontroller. And control pins RS, RW and E to the pins 12,13,14 (pins 2,3,4 of port 3) of the microcontroller, respectively.

Power Supply and Contrast Adjustment Setup

PIN 2(VDD) and PIN 15(Backlight supply) of the LCD are connected to a voltage (5V), and PIN 1 (VSS) and PIN 16(Backlight ground) are connected to ground.

Pin 3(V0) is connected to the voltage (Vcc) through a variable resistor of 10k to adjust the contrast of the LCD. The middle leg of the variable resistor is connected to PIN 3, and the other two legs are connected to the voltage supply and Ground.

 

LCD Interfacing with 8051 C Program Explanation

I have tried to explain the code through comments (in the code itself).

As I have explained earlier about command mode and data mode, you can see that while sending a command (function lcd_cmd), we have set RS=0, RW=0 and a HIGH to LOW pulse is given to E by making it 1, then 0. Also, when sending data (function lcd_data) to LCD, we have set RS=1, RW=0 and a HIGH to LOW pulse is given to E by making it 1 to 0. Function msdelay() has been created to create a delay in milliseconds and is called frequently in the program, it is called so that the LCD module can have sufficient time to execute the internal operations and commands.

 

A while loop has been created to print the string, which calls the lcd_data function each time to print a character until the last character (null terminator- ‘\0’).

We have used the LCD_init () function to get the LCD ready by using the preset command instructions (explained above). 

 

Typical Problems and Solutions

Problem: LCD displays covered in black squares (or no display at all) 
Solution:  Check power connections and adjust contrast with the variable resistor.  Ensure that Vcc is +5V.

Problem: Garbage characters are displayed
Solution:  Check data line connections, make sure the lcd_init() function has the proper initialisation sequence.

Problem: LCD not responding to commands
Solution:  Check RS, RW, and E control pin connections.  Check the timing of the enable pulse in your code.

Problem: Characters are displayed but scrambled
Solution: Increase the delay values in the msdelay() function, and check that the correct command/data mode is used when switching between modes.

 

Frequently Asked Questions 

⇥ Why does my LCD have a blank screen with the 8051? 
Nothing appearing on the LCD for 8051 interfacing would typically indicate that we have incorrect power connections (as an example, check to make sure +5V is connected where VDD is located), we have not set the contrast correctly (remember to use the variable resistor at 10kΩ), we forgot to issue the initialization commands, or we connected the LCD wrong. We can check all connections (i.e., we powered the correct pins of the LCD), check the power supply (ensure that it is +5V), and ensure that we called the lcd_init() function before we wrote anything to the LCD.

⇥ What are the basic LCD commands for 8051 programming?
The basic LCD commands for 8051 programming are: 0x38 (function set - 2 lines, 5x7 matrix), 0x0C (display ON, cursor off), 0x06 (entry mode - increment cursor), 0x01 (clear display), 0x80 (cursor to line 1), and 0xC0 (cursor to line 2). With all the above commands, we can initialise and control the LCD in the long term.

⇥ How do I display text on the LCD using the 8051 microcontroller?
In order to write text on an LCD using the 8051, we first need to call lcd_init() to initialise the LCD, and then we need to write each character using the lcd_data() function and with RS=1 (data mode). This can be done in a loop to add the complete string character by character until a null terminator is received. If I want to write in the first line, I send the command 0x80 to set the cursor in the first line. The same is done with 0xC0 for the second line.

⇥  What is the difference between 4-bit and 8-bit interfacing an LCD with 8051?
With 8-bit interfacing of an LCD with 8051, all 8 data pins (D0-D7) are used, so 11 microcontroller pins are used in total. In 4-bit interfacing, only the upper 4 pins are used (D4-D7), so I only use 7 pins. The benefit is that I save I/O ports. I send the data in 4-bit mode in 2 nibbles, so it is more complicated code, but it saves my pins. In 8-bit mode, it is much simpler code and 8 pins are removed from the schematic. 

GitHub Repository

Explore More LCD Interfacing Projects

Deepen your understanding of 16x2 LCD modules by diving into these diverse microcontroller-based interfacing projects.

// Program for LCD Interfacing with 8051 Microcontroller (AT89S52) 
#include<reg51.h>
#define display_port P2      //Data pins connected to port 2 on microcontroller
sbit rs = P3^2;  //RS pin connected to pin 2 of port 3
sbit rw = P3^3;  // RW pin connected to pin 3 of port 3
sbit e =  P3^4;  //E pin connected to pin 4 of port 3
void msdelay(unsigned int time)  // Function for creating delay in milliseconds.
{
    unsigned i,j ;
    for(i=0;i<time;i++)    
    for(j=0;j<1275;j++);
}
void lcd_cmd(unsigned char command)  //Function to send command instruction to LCD
{
    display_port = command;
    rs= 0;
    rw=0;
    e=1;
    msdelay(1);
    e=0;
}
void lcd_data(unsigned char disp_data)  //Function to send display data to LCD
{
    display_port = disp_data;
    rs= 1;
    rw=0;
    e=1;
    msdelay(1);
    e=0;
}
 void lcd_init()    //Function to prepare the LCD  and get it ready
{
    lcd_cmd(0x38);  // for using 2 lines and 5X7 matrix of LCD
    msdelay(10);
    lcd_cmd(0x0F);  // turn display ON, cursor blinking
    msdelay(10);
    lcd_cmd(0x01);  //clear screen
    msdelay(10);
    lcd_cmd(0x81);  // bring cursor to position 1 of line 1
    msdelay(10);
}
void main()
{
    unsigned char a[15]="CIRCUIT DIGEST";    //string of 14 characters with a null terminator.
    int l=0;
    lcd_init();
    while(a[l] != '\0') // searching the null terminator in the sentence
    {
        lcd_data(a[l]);
        l++;
        msdelay(50);
    }
}