LPC2148 – LCD Interfacing

Last Updated on: June 29th, 2022

This article is a continuation of the series of tutorials on the LPC2148 Microcontroller (ARM7). The aim of this series is to provide easy and practical examples that anyone can understand. In the previous tutorial, we have seen LPC2148 (ARM7) ADC. In our last tutorial, we have seen LED and Switch interfacing. Now we are going to see LCD interfacing with LPC2148.

LCD Interfacing with LPC2148

LCD DISPLAY

We always use devices made up of Liquid Crystal Displays (LCDs) like computers, digital watches, and also DVD and CD players. They have become very common and have taken a giant leap in the screen industry by clearly replacing the use of Cathode Ray Tubes (CRT). CRT draws more power than LCD and is also bigger and heavier. All of us have seen an LCD, but no one knows the exact working of it. Let us take a look at the working of an LCD.

Here we are using alphanumeric LCD 16×2. A 16×2 LCD display is a very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi-segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations, and so on.

A 16×2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in a 5×7 pixel matrix. This LCD has two registers, namely, Command and Data. The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling the display, etc. The 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.

Pin Diagram

Pin Description

 

Pin No	Function	Name
1	Ground (0V)	Ground
2	Supply voltage; 5V (4.7V – 5.3V)	Vcc
3	Contrast adjustment; through a variable resistor	VEE
4	Selects command register when low; and data register when high	Register Select
5	Low to write to the register; High to read from the register	Read/write
6	Sends data to data pins when a high to low pulse is given	Enable
7	8-bit data pins	DB0
8		DB1
9		DB2
10		DB3
11		DB4
12		DB5
13		DB6
14		DB7
15	Backlight VCC (5V)	Led+
16	Backlight Ground (0V)	Led-

The LCD display module requires 3 control lines as well as either 4 or 8 I/O lines for the data bus. The user may select whether the LCD is to operate with a 4-bit data bus or an 8-bit data bus. If a 4-bit data bus is used the LCD will require a total of 7 data lines (3 control lines plus the 4 lines for the data bus). If an 8-bit data bus is used the LCD will require a total of 11 data lines (3 control lines plus the 8 lines for the data bus).

The three control lines are referred to as EN, RS, and RW.

The EN line is called “Enable.” This control line is used to tell the LCD that you are sending it data. To send data to the LCD, your program should make sure this line is low (0) and then set the other two control lines and/or put data on the data bus. When the other lines are completely ready, bring EN high (1) and wait for the minimum amount of time required by the LCD datasheet (this varies from LCD to LCD), and end by bringing it low (0) again.

The RS line is the “Register Select” line. When RS is low (0), the data is to be treated as a command or special instruction (such as clear screen, position cursor, etc.). When RS is high (1), the data being sent is text data which should be displayed on the screen. For example, to display the letter “T” on the screen you would set RS high.

The RW line is the “Read/Write” control line. When RW is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively querying (or reading) the LCD. Only one instruction (“Get LCD status”) is a read command. All others are writing commands–so RW will almost always be LOW.

Finally, the data bus consists of 4 or 8 lines (depending on the mode of operation selected by the user). In the case of an 8-bit data bus, the lines are referred to as DB0, DB1, DB2, DB3, DB4, DB5, DB6, and DB7.

LCD COMMANDS

Now let’s move to the program.

Connections

RS – P0.8

RW – P0.9

EN – P0.10

Data lines –  P0.1 – P0.7

CODE

#include<lpc214x.h>

#define bit(x) (1<<x)
#define delay for(i=0;i<1000;i++);

unsigned int i;

void lcd_int();
void dat(unsigned char);
void cmd(unsigned char);
void string(unsigned char *);

void main()
{
    IO0DIR|=0XFFF;
    lcd_int();
    cmd(0x8a);
    string("EMBETRONICX.COM ");
    while(1) {
        cmd(0x18);
        delay;
    }
}

void lcd_int()
{
    cmd(0x30);
    cmd(0x0c);
    cmd(0x06);
    cmd(0x01);
    cmd(0x80);
}

void cmd(unsigned char a)
{
    IO0PIN&=0x00;
    IO0PIN|=(a<<0);
    IO0CLR|=bit(8);                //rs=0
    IO0CLR|=bit(9);                //rw=0
    IO0SET|=bit(10);               //en=1
    delay;
    IO0CLR|=bit(10);               //en=0
}

void dat(unsigned char b)
{
    IO0PIN&=0x00;
    IO0PIN|=(b<<0);
    IO0SET|=bit(8);                //rs=1
    IO0CLR|=bit(9);                //rw=0
    IO0SET|=bit(10);               //en=1
    delay;
    IO0CLR|=bit(10);               //en=0
}

void string(unsigned char *p)
{
    while(*p!='\0') {
        dat(*p++);
    }
}

OUTPUT – LCD Interfacing with LPC2148

[ Please find the output image Here ]

In our next tutorial, we will see how to print the custom character using LPC2148 (ARM7). If you want to use FreeRTOS on LPC2148, then please refer FreeRTOS series.

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