HOW TO WRITE YOUR OWN CODE FOR AN LCD DISPLAY (16X2 OR 16X4)

The Arduino ide default comes with an excellent library with examples for LCD display it’s really easy! One to use.

Mine is not best one but the reason behind this post is to experience the feel of writing your own code and understanding the embedded displays and their working technology and how they works with u-controllers, maybe in future it can helps you to write a code for lcd display with other new microcontrollers or other programming languages.

So let’s start with the one important things:

The datasheet is your friend in this quest for any quest, for real! So getting the data sheet is important here I’m using a 16x2 LCD. This kind LCD is based on parallel interface LCD controller chip from Hitachi called the HD44780.

Next is physical pinout the display uses a matrix of dots and displays only characters in 16x2 matrixes. Each character is displayed in a 5 column × 8 row dot matrix or a 5 column × 10 row dot matrix

The pinout is LCD has totally 16 pins they are:

1. GND: used for GND purpose the –ve connection.

2. VCC: used for VCC purpose the +Ve connection.

3. VSS: used for the potentiometer output voltage (0-5V), this voltage is used to control the contrast of LCD.

4. RS: “REGISTER CONTROL” used for to control the register to whether send data or send commands to LCD display. The HD44780 has two registers: an Instruction Register (IR) and a Data Register (DR).

If RS_PIN is written as HIGH then it in data mode and we can write data/characters, if it is written LOW then it is in command mode.

5. R/W_PIN: used for whether to read from or write to LCD Register. If you want to read from lcd register set it HIGH, since we only want it write so Pull it to GND hence LOW sets in write mode.

6. Enable: used to enable the LCD, when it is set to LOW LCD doesn’t care if you are sending data or commands, so usually we set it to HIGH for LCD to work.

7. D0-D7_PINS: used to write data to LCD, the D0 to D7 pins are 8-BIT data transfer lines hence we can either use whole 8 pins for data or just use 4 pins D4-D8 to send data in nibble (4-bits) at a time.

LCDs are designed in a way that we can talk to the LCD using only 4 data pins(4-bit mode) instead of 8(8-bit mode). This saves us 4 pins!

8. A_PIN: used as ANODE +ve connection for backlight

9. K_PIN: used as KATHODE –ve connection for backlight

If we insert a potentiometer between A and K we control the Backlit brightness.

Here are the commands for lcd display 16x2:

 

Sr.No.	Hex Code	Command to LCD instruction Register
1	01	Clear display screen
2	02	Return home
3	04	Decrement cursor (shift cursor to left)
4	06	Increment cursor (shift cursor to right)
5	05	Shift display right
6	07	Shift display left
7	08	Display off, cursor off
8	0A	Display off, cursor on
9	0C	Display on, cursor off
10	0E	Display on, cursor blinking
11	0F	Display on, cursor blinking
12	10	Shift cursor position to left
13	14	Shift cursor position to right
14	18	Shift the entire display to the left
15	1C	Shift the entire display to the right
16	80	Force cursor to beginning ( 1st line)
17	C0	Force cursor to beginning ( 2nd line)
18	38	2 lines and 5×7 matrix

 

That being said lets write our own code:

#define lcd_dpins PORTD

/*

const unsigned int d0 = 1;

const unsigned int d4 = 2;

const unsigned int d4 = 3;

const unsigned int d4 = 4;

const unsigned int d4 = 5;

const unsigned int d5 = 6;

const unsigned int d6 = 7;

const unsigned int d7 = 8;

*/

const unsigned int RS = 9;

const unsigned int RW = 10;

const unsigned int EN = 11;

void lcd_cmd(char cmd)

{

  digitalWrite(RS,LOW);

  digitalWrite(RW,LOW);

  digitalWrite(EN,HIGH);

  delay(2);

  digitalWrite(RS,LOW);

  delay(5);

  }

void lcd_on()

{ 

  delay(20);    /* LCD Power ON Initialization time >15ms */

  lcd_cmd(0x38); /* Initialization of 16X2 LCD in 8bit mode */

  lcd_cmd(0x0C); /* Display ON Cursor OFF */

  lcd_cmd(0x06); /* Auto Increment cursor */

  lcd_cmd(0x01); /* clear display */

  lcd_cmd(0x80); /* cursor at home position */

}

void lcd_char(unsigned char char_data)

{

  lcd_dpins = char_data;

  digitalWrite(RS,HIGH);

  digitalWrite(RW,LOW);

  digitalWrite(EN,HIGH);

  delay(2);

  digitalWrite(RS,LOW);

  delay(5);

  }

 void lcd_string(unsigned char *str)

 {

  int i=0;

  for(i=0;str[i]!=0;i++)

  {

    lcd_char(str[i]);

    }

  }

 void lcd_pos(char x, char y ,char *str)

{

 if (x == 0)

  lcd_cmd((y & 0x0F)|0x80);

  else if (x == 1)

  lcd_cmd((y & 0x0F)|0xC0);

  lcd_string(str);  /* Call LCD string function */

}

void setup()

{

  DDRD = B11111111;

  DDRB = B11001110;

  }

void loop()

{

  lcd_on();

  lcd_string("Hi");

  lcd_cmd(0xc0);

  lcd_string("hello world");

}