LCD (Liquid Crystal Display):
LCD screen is an electronic display module and find a wide range of applications. A 16x2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segment and other multi segment LED's. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom character (unlike in seven segments), animation and so on. 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, 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 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. Click to learn more about internal structure of a LCD.
Block Diagram of LCD:
LCD stands for liquid crystal display. They come in many sizes 8x1 , 8x2 ,10x2, 16x1 , 16x2 , 16x4 , 20x2 , 20x4 ,24x2 , 30x2 , 32x2 , 40x2 etc . Many multinational companies like Philips Hitachi Panasonic make their own special kind of lcd's to be used in their products. All the lcd’s performs the same functions (display characters numbers special characters ASCII characters etc).Their programming is also same and they all have same 14 pins (0-13) or 16 pins (0 to 15).
ALL LCDs have
- Eight(8) Data pins
- VCC (Apply 5v here)
- GND (Ground this pin)
- RS (Register select)
- RW (read - write)
- EN (Enable)
- V0 (Set Lcd contrast)
- 8-Data pins carries 8-bit data or command from an external unit such as microcontroller.
Lcd have two registers:
1 1 Command Register
2 Data Register
1) Command Register: When we send commands to lcd these commands go to Command register and are processed there. Commands with their full description are given in the picture below.
When RS=0 Command Register is Selected.
2) Data Register: When we send Data to lcd it goes to data register and is processed their.
When RS=1 Data Register is selected.
16×2 LCD module commands:
16×2 LCD module has a set of preset command instructions. Each command will make the module to do a particular task. These commands are very important for displaying data in LCD. The list of commands given below:
Command
|
Function
|
0F
|
For switching on LCD, blinking the cursor.
|
1
|
Clearing the screen
|
2
|
Return home.
|
4
|
Decrement cursor
|
6
|
Increment cursor
|
E
|
Display on and also cursor on
|
80
|
Force cursor to beginning of the first line
|
C0
|
Force cursor to beginning of second line
|
38
|
Use two lines and 5x7 matrix
|
83
|
Cursor line 1 position 3
|
3C
|
Activate second line
|
0C3
|
Jump to second line position 3
|
0C1
|
Jump to second line position1
|
LCD initialization:
The steps that has to be done for initializing the LCD display is given below and these steps are common for almost all applications.
§ Send 38H to the 8 bit data line for initialization
§ Send 0FH for making LCD ON, cursor ON and cursor blinking ON.
§ Send 06H for incrementing cursor position.
§ Send 01H for clearing the display and return the cursor.
Sending data to the LCD:
The steps for sending data to the LCD module is given below. I have already said that the LCD module has pins namely RS, R/W and E. It is the logic state of these pins that make the module to determine whether a given data input is a command or data to be displayed.
- Make R/W low.
- Make RS=0 if data byte is a command and make RS=1 if the data byte is a data to be displayed.
- Place data byte on the data register.
- Pulse E from high to low.
- Repeat above steps for sending another data.
Interfacing of lcd 4 bit with AVR
#include <avr/io.h>
#include<util/delay.h>
#define rs PA0
#define rw PA1
#define en PA2
void CMD()
{
PORTA&=~(1<<rs);
PORTA&=~(1<<rw);
PORTA|=(1<<en);
_delay_ms(400);
PORTA&=~(1<<en);
}
void display()
{
PORTA|=(1<<rs);
PORTA&=~(1<<rw);
PORTA|=(1<<en);
_delay_ms(400);
PORTA&=~(1<<en);
}
int main(void)
{int j,i,k;
unsigned char a[]={0x02,0x28,0x0e,0x01,0x80,0x06};
char b[]={"welcome to all"};
char c[]={"GOD BLESS U "};
while(1)
{
DDRA=0xFF;
for(i=0;i<=5;i++)
{
PORTA=(a[i]&0xF0);
CMD();
PORTA=((a[i]<<4)&0xF0);
CMD();
}
for(j=0;j<=14;j++)
{
PORTA=(b[j]&0xF0);
display();
PORTA=((b[j]<<4)&0xF0);
display();
}
PORTA=(0xC0&0xF0);
CMD();
PORTA=((0xC0<<4)&0xF0);
CMD();
for(k=0;k<=15;k++)
{
PORTA=(c[k]&0xF0);
display();
PORTA=((c[k]<<4)&0xF0);
display();
}
}
}
