Electronic – Controlling an LCD device using serial I2C module

lcd

I purchased an LCD/I2C driver pair and have been trying to get the thing to initialize. I am able to communicate with the I2C driver without issue, but getting the correct initialization sequence has proven to be a real pain.

This is the module and LCD I have: LCD and Driver

The LCD is shown as type 2004A and has J204A etched on the back.

enter image description here

I have read that this particular driver makes use of the LCD 4-bit mode and has the following physical connections to the LCD module (from the link above).

From the schematic, you can derive that:

P0: RS

P1: RW

P2: CS

P3: BL

P4: D4

P5: D5

P6: D6

P7: D7

Considering that data frames are sent (neglecting the ACK, start, and stop) MSB, I would presume that the MSB of the byte shifted into this device is represented at its output as P7 (I could not directly find this in the datasheet, but after a bit of testing it appears true).

Now, with all that aside and after successfully addressing (and receiving an ACK bit) from the I2C driver, one must initialize the LCD module in 4 bit mode and set other parameters – this is where I am completely stuck.

I have written the following init sequence that simply does not work:

void lcdInit(void){
_delay_ms(20); 

//D7 D6 D5 D4 BL CS RW RS
// x  x  x  x  1  1  0  0 = XC (hex)
    i2c_write(0x2C); _delay_us(4200);
    i2c_write(0x8C); _delay_us(4200); //0x28

    i2c_write(0x2C); _delay_us(120);
    i2c_write(0x8C); _delay_us(120);  //0x28

    i2c_write(0x2C); _delay_us(50);   //0x28
    i2c_write(0x8C); _delay_us(50);   //4 bit mode, N=1(2lines), F=0(5x8)

    i2c_write(0x0C); _delay_us(50);   //0x06
    i2c_write(0x6C); _delay_us(50);   //I/D=1(increment), S=0(display shift off)

    i2c_write(0x0C); _delay_us(50);   //0x0C
    i2c_write(0xCC); _delay_us(50);   //Display on, cursor off, blink off

    i2c_write(0x0C); _delay_us(1700);  //clear display
    i2c_write(0x1C); _delay_us(1700);  //0x01
}

I know that each byte sent has the correct format (i.e. 0 0 1 DL N F X X ), but nothing was said regarding the ordering of such statements.

This sequence seemed most logical:

Funtion Set (4-bit)

Entry Mode (shifting, etc)

Commands (state variables)

Any ideas?

Best Answer

#define ON  1
#define OFF 0

//#define __LCD2__  // 2 row display
#define __LCD4__  // 4 row display

#ifdef __LCD2__
  #define LCD_MAX_LINES  2  // usually a 1602 2 X 16
  #define LCD_DISPLAY_WIDTH 16
  #define LCD_ID 0x4E       // I2C Base address for this interface
#endif

#ifdef __LCD4__
  #define LCD_MAX_LINES  4  // usually a J204A 4 X 20
  #define LCD_DISPLAY_WIDTH 20
  #define LCD_ID 0x40       // I2C Base address for this interface
#endif

#define RS          0b00000001  //P0 - PCF8574T Pin connected to RS
#define RW          0b00000010  //P1 - PCF8574T Pin connected to RW
#define EN          0b00000100  //P2 - PCF8574T Pin connected to EN
#define BACKLIGHT   0b00001000  //P3 - PCF8574T Pin connected to BACKLIGHT

#define LCD_LINE1   0x80        // LCD RAM address for line 1
#define LCD_LINE2   0xC0        // LCD RAM address for line 2
#define LCD_LINE3   0x94        // LCD RAM address for line 3
#define LCD_LINE4   0xD4        // LCD RAM address for line 4

int LcdBacklight = ON;

void InitLCD(void)
{
    printf("Initializing LCD...\r\n");

    delay_ms(500); //LCD power up delay

    LcdSendByte(0x00);
    LcdSendByte(0x10);
    LcdSendByte(0x00);
    LcdSendByte(0x00);
    LcdSendByte(0x10);

    //First state in 8 bit mode
    LcdSendByte(0x30);
    LcdSendByte(0x30);

    //Then set to 4-bit mode
    LcdSendByte(0x30);
    LcdSendByte(0x20);

    //mode 4 bit, 2 lines, characters 5 x 7
    LcdSendByte(0x20);
    LcdSendByte(0x80);

    //no need to have the cursor on. 
    //but if you want then '0Ch' is the addr
    LcdSendByte(0x00);
    LcdSendByte(0xC0);

    //the cursor moves to the left (06h)
    LcdSendByte(0x00);
    LcdSendByte(0x60);

    printf("LCD   Initialized...\r\n");
}
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