Robotics INDIA: August 2009

LCD Interfacing with Atmega16

LCD display:

The display used here is 16x2 LCD (Liquid Crystal Display); this means 16 characters per line by 2 lines. A very popular standard exists which allows us to communicate with the vast majority of LCDs regardless of their manufacturer. The standard is referred to as HD44780U, which refers to the controller chip which receives data from an external source (in this case, the Atmega16) and communicates directly with the LCD. The 44780 standard requires 3 control lines as well as either 4 or 8 I/O lines for the data bus. Here we are using 8-bit mode of LCD, i.e., using 8-bit 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 we are sending it data. To send data to the LCD, our 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 write commands--so RW will almost always be low.

In our case of an 8-bit data bus, the lines are referred to as DB0, DB1, DB2, DB3, DB4, DB5, DB6, and DB7.

Fig: 16X2 LCD display

Function	Pin Number	Name	Logic State	Description
Ground	1	Vss	-	0V
Power supply	2	Vdd	-	+5V
Contrast	3	Vee	-	0 - Vdd
Control of operating	4	RS	0 1	D0 – D7 are interpreted as commands D0 – D7 are interpreted as data
	5	R/W	0 1	Write data (from controller to LCD) Read data (from LCD to controller)
	6	E	0 1 From 1 to 0	Access to LCD disabled Normal operating Data/commands are transferred to LCD
Data / commands	7	D0	0/1	Bit 0 LSB
	8	D1	0/1	Bit 1
	9	D2	0/1	Bit 2
	10	D3	0/1	Bit 3
	11	D4	0/1	Bit 4
	12	D5	0/1	Bit 5
	13	D6	0/1	Bit 6
	14	D7	0/1	Bit 7 MSB

Table: Pin description of LCD

LCD Circuit:

lcd1

To Pin 4,5,6 To PortA

Of PortD

Fig: LCD Connections

Testing (D.C. Conditions):

PIN 7 to 14 are data pins.
Voltage at pin 2 is +5.00V
Pin 3 is connected to 10K variable resistance for contrast setting.

Pin 4, 5, 6 are control lines connected to PORT D.

Actual circuit diagram is similar to the LCD connections in this CIRCUIT.

LCD Basic Commands:

No.	Instruction	Hex	Decimal
1	Function Set: 8-bit, 1 Line, 5x7 Dots	0x30	48
2	Function Set: 8-bit, 2 Line, 5x7 Dots	0x38	56
3	Function Set: 4-bit, 1 Line, 5x7 Dots	0x20	32
4	Function Set: 4-bit, 2 Line, 5x7 Dots	0x28	40
5	Entry Mode	0x06	6
6	Display off Cursor off (clearing display without clearing DDRAM content)	0x08	8
7	Display on Cursor on	0x0E	14
8	Display on Cursor off	0x0C	12
9	Display on Cursor blinking	0x0F	15
10	Shift entire display left	0x18	24
12	Shift entire display right	0x1C	30
13	Move cursor left by one character	0x10	16
14	Move cursor right by one character	0x14	20
15	Clear Display (also clear DDRAM content)	0x01	1
16	Set DDRAM address or cursor position on display	0x80+add	128+add
17	Set CGRAM address or set pointer to CGRAM location	0x40+add	64+add

Programming Steps Sequence:

1) Initialize the LCD.

2) Select the command or instruction register (RS=0 or RS=1).

3) Set RW low (to write to LCD).

4) Send a high to low pulse on EN pin.

5) Check if the LCD is busy (Optional Step, it eliminates the delay issue).

6) Move to instruction or command function.

7) Repeat above steps.

The Source Code:

/*Every relevant command is included with a detailed and explanatory comment, if you still encounter any problem in the code feel free to post your queries*/

/* Platform: WINAVR*/

/*This code simply prints RoboZeal on LCD*/

#define F_CPU 12000000 //Change the F_CPU value to that you're using in your hardware, I used 12Mhz

#include <avr/io.h>

#include <util/delay. h>

#define dataport PORTA

#define commport PORTD

#define rs PD4

#define wr PD5

#define en PD6

int LCD_init(void);

int LCD_SendData(void);

int wrcomm(void);

int wrdata(void);

int main(void)

{

DDRA = 0xFF; //Set PortA as output port

DDRD = 0x70 //Set PortD 4, 5, 6 pin as output pins

LCD_init(); //Initialise LCD

LCD_SendData( ); //Write to LCD

return 1;

}

int LCD_init()

{

dataport = 0x38; //initialize LCD 2 lines, 5x7 matrix