LCD Interfacing with AVR

Interfacing LCD Display in 8bit Mode

I’ve already discussed about the LCD display in a note here in this website. You can read the Note on character LCD Display here. Now let us come to the interfacing side of LCD. Let us see the 8bit mode interfacing of the LCD display with an AVR micro controller first. I have added two circuits in this post 1) Interfacing LCD with Avr Atmega8 and 2) Interfacing with Atmega32. Towards the end you can see the real life display as an image where I displayed characters“Circuits Today” ?
Here to interface LCD with Avr, an 8 bit data bus is required. In addition we need 2 bit control bus for write only mode or 3 bit control bus for Read plus write mode. Connect pin 1 of the LCD module to ground, pin 2 to +ve supply. Connect a Pot (2 to 5 K Ohm) across the supply and ground. Connect the middle pin of the pot to pin3 of LCD module. If you want to light up the back light, connect the –LED pin to ground. Connect the +LED pin of the LCD to the +ve supply using a resistor. Figure below is the two circuit diagrams!

Now, I’ve written up two routines for two separate cycles. One is used to transfer data (or character). Another sends command. In C code, they are listed under the functions ‘LCD()’ and ‘LCDcmd()’ respectively. To prevent crash of data, we must allow the LCD to complete execution of each operation. Here we will be using delay loops available from the AVR studio Library. Each instruction or data takes at least 40uS to get executed. Longest wait loop is of 1.65mS. For further details, read my note upon LCD display (Wait a minute. It shouldn’t be ‘LCD display’, instead ‘LC display’. But ‘LCD display’ is widely used ) & AVR Library overview for beginners. Let’s check the code
One more thing, it is better that to copy and paste this code in notepad (Or word pad or MS word) and check this code.
//-------------------------------------------------------- Start
#include
#include
#define DPORT PORTB //Define Data port
#define DPDDR DDRB
#define CPORT PORTD //Define Signals port
#define CPDDR DDRD
#define RS PD6 //Signal Pins, Reset
#define EN PD7 //Signal Pins, Enable
//Pre-defining Commands
#define LCDClear 0x01 //Clears LCD Display
#define LCD8bit 0x38 //Sets up LCD in 8bit mode
#define LCDCursorOn 0x0f //Enables Cursor
#define LCDSeek00 0x80 //Seeks the pointer to the begeining
void LCD(char ch);
void LCDcmd(void);
void LCDInitialize(void);
int main()
{ DPDDR=0xff;
CPDDR=0xf0;
_delay_ms(2000);
LCDInitialize();
LCD(‘C’);
LCD(‘i’);
LCD(‘r’);
LCD(‘c’);
LCD(‘u’);
LCD(‘i’);
LCD(‘t’);
LCD(‘s’);
LCD(‘ ’);
LCD(‘T’);
LCD(‘o’);
LCD(‘d’);
LCD(‘a’);
LCD(‘y’);
return 0;
}
void LCD(char ch)
{ DPORT=ch; //Put values to ports
CPORT=(1<<RS)|(1<<EN); //Signaling to send data
_delay_us(10);
CPORT=(1<<RS)|(0<<EN);
_delay_us(45);
}
void LCDcmd(char ch)
{ DPORT=ch;
CPORT=(0<<RS)|(1<<EN); //Signaling to send commands
_delay_ms(10);
CPORT=(0<<RS)|(0<<EN);
_delay_ms(45);
if(ch==0x01||ch==0x02) // If commands are LCD Clear or
// LCDSeek00, delay 2mS
_delay_ms(2);
}
void LCDInitialize(void)
{ LCDcmd(LCD8bit);
LCDcmd(LCDCursorOn);
LCDcmd(LCDClear);
LCDcmd(LCDSeek00);
}
//-------------------------------------------------------- End

Now I’ve used Lots of crazy symbols in my program. Here is a summary.

• In C, ‘0x’ prefix represents a hexadecimal number. ‘0b’ represents binary.

• ‘|’ is the bitwise ‘OR’ operation. Here, 0b0010|0b0110=0b0110.

• ‘||’ is the Logical ‘OR’ test. If in statement ‘A||B’, if value of either or both of the operand is NOT Zero (or True), then the statement result is TRUE.

• ‘≪’ stands for Bitwise right shift operation. Here, 0b0001≪2 =0b0100.

• ‘≫’ stands for Bitwise left shift operation. Here, 0b1000≫1 =0b0100. Just for your knowledge, I’ve not used them in this article.

So that was basic version of the code. Let’s see some better functions to be compiled.
//-------------------------------------------------------- Start
#include
#include
#define DPORT PORTB //Define Data port
#define DPDDR DDRB
#define CPORT PORTD //Define Signals port
#define CPDDR DDRD
#define RS PD6 //Signal Pins, Reset
#define EN PD7 //Signal Pins, Enable
#define LCDClear 0x01 //Clears LCD Display
#define LCD8bit 0x38 //Sets up LCD in 8bit mode
#define LCDCursorOn 0x0f //Enables Cursor
#define LCDSeek00 0x80 //Seeks the pointer to the begeining
void LCD(char ch);
void LCDcmd(void);
void LCDInitialize(void);
void printStringLCD(char *str);
int printIntLCD(unsigned int i);
int main()
{ DPDDR=0xff;
CPDDR=0xf0;
_delay_ms(500);
LCDInitialize();
printStringLCD(“Circuits Today”);
_delay_ms(5000);
LCDcmd(LCDClear);
prinStringLCD(“Print an Integer”);
LCDcmd(0xc0);
printIntLCD(990);
return 0;
}
void LCD(char ch)
{ DPORT=ch; //Put values to ports
CPORT=(1<<RS)|(1<<EN); //Signaling to send data
_delay_us(10);
CPORT=(1<<RS)|(0<<EN);
_delay_us(45);
}
void LCDcmd(unsigned char ch)
{ DPORT=ch;
CPORT=(0<<RS)|(1<<EN); //Signaling to send commands
_delay_us(10);
CPORT=(0<<RS)|(0<<EN);
_delay_us(45);
if(ch==0x01||ch==0x02)
_delay_ms(2);
}
void LCDInitialize(void)
{ LCDcmd(LCD8bit);
LCDcmd(LCDCursorOn);
LCDcmd(LCDClear);
LCDcmd(LCDSeek00);
}
void printStringLCD(char *str)
{ int i=0;
while(str[i]!='\0')
{ DPORT=str[i]; //Put values to ports
LCD(ch);
i++;
}
}
int printIntLCD(unsigned int i)
{ static int a;
a=0;
if(i!=0)
{ printIntLCD(i/10);
LCD(‘0’+i%10);
a++;
}
return a;
}
//-------------------------------------------------------- End

For more detail: LCD Interfacing with AVR