Liquid Crystal Display (LCD)

Introduction

The 16x2 LCD module (HD44780 controller) is commonly used in embedded systems to display text. It shows 16 characters per line on 2 lines. This guide explains how to interface it with the TM4C123 microcontroller using the efficient 4-bit mode.

LCD Basics

• Registers:

  • Command Register: Sends instructions (e.g., clear display).
  • Data Register: Sends characters to display.

• Control Pins:

  • RS: Selects command or data register.
  • RW: Selects read or write mode.
  • E: Enables data latch.

• Data Pins:

  • D0-D7: Used to send data; in 4-bit mode only D4-D7 are used.

Important

Data is sent in two parts: first the upper 4 bits, then the lower 4 bits.Each 8-bit. value requires two writes, toggling the E pin after each to latch the data.

Initialization Steps (4-bit Mode)

1. Set RS, RW, E to low and wait 40 ms after power-on.

2. Send command 0x30 (upper nibble only) three times with delays (>4.1 ms, >100 μs, >100 μs).

3. Send 0x20 (upper nibble only) to switch to 4-bit mode.

4. Send full commands:

   • 0x28: 4-bit mode, 2 lines, 5x7 dots
   • 0x0C: Display on, cursor off, blink off
   • 0x06: Increment cursor, no display shift
   • 0x01: Clear display
   • 0x02: Return home

Note

Steps 2-3 send only the upper nibble since LCD isn’t in 4-bit mode yet. After step 3, send full 8-bit commands in two nibbles.

LCD Commands

Command	Hex Range	Description & Details
Clear Display	0x01	Clears screen, sets cursor to home (address 0).
Return Home	0x02	Cursor returns to home (address 0).
Entry Mode Set	0x04–0x07	Controls cursor move direction & display shift:
		- 0x04: cursor moves left, no shift
		- 0x06: cursor moves right, no shift (default)
		- Others enable display shift while moving cursor
Display Control	0x08–0x0F	Turns display, cursor, and blink on/off:
		- 0x08: display off
		- 0x0C: display on, cursor off
		- 0x0E: display and cursor on
		- 0x0F: display, cursor, and blink on
Cursor/Display Shift	0x10–0x1F	Shifts cursor or display left or right.
	0x18	Shift display left
	0x1C	Shift display right
Set DDRAM Address	0x80 + addr	Moves cursor to DDRAM address (e.g., 0x80 start of 1st line, 0xC0 start of 2nd line).
Function Set	0x20–0x3F	Sets interface parameters (bit flags):
		- Bit 4: Data length (0=4-bit, 1=8-bit)
		- Bit 3: Number of lines (0=1 line, 1=2 lines)
		- Bit 2: Font type (0=5x8 dots, 1=5x10 dots)
		Example: 0x28 = 4-bit, 2 lines, 5x8 font

Example Code

main.c

#include "TM4C123.h"
#include "lcd.h"




int main(void)
{

    LCD_Init();
    LCD_Clear();        // Ensure display is clear
    LCD_SetCursor(0,0); // Set cursor to beginning
	LCD_Print("ENCS4110 Lab");
    
    while(1)
    {	
    }
}

lcd.c

#include "lcd.h"

#define SYSTEM_CLOCK_HZ 50000000 // 50 MHz system clock
#define CYCLES_PER_US   (SYSTEM_CLOCK_HZ / 1000000)



//====================[ SysTick Delay Functions ]====================
void SysTick_Init(void)
{
    SysTick->CTRL = 0;
    SysTick->LOAD = CYCLES_PER_US - 1;  // 1us delay at 50MHz
    SysTick->VAL = 0;
    SysTick->CTRL = 0x5;     // Enable with system clock
}

void delay_us(int us)
{
    SysTick->LOAD = (CYCLES_PER_US * us) - 1;
    SysTick->VAL = 0;
    SysTick->CTRL = 0x5; // Enable with system clock
    while ((SysTick->CTRL & 0x10000) == 0);
    SysTick->CTRL = 0;
}

void delay_ms(int ms)
{
    while (ms--)
        delay_us(1000);
}

//====================[ LCD Helper Functions ]====================
void LCD_EnablePulse(void)
{
    delay_us(1);
    GPIOB->DATA |= EN;
    delay_us(1);
    GPIOB->DATA &= ~EN;
    delay_us(1);
}

void LCD_SendNibble(unsigned char nibble)
{
    // Send nibble to PB4–PB7
    GPIOB->DATA = (GPIOB->DATA & ~DATA_MASK) | ((nibble << 4) & DATA_MASK);
    LCD_EnablePulse();
}

//====================[ LCD Initialization ]====================
void LCD_Init(void)
{
    // Enable clock to PORTB
    SYSCTL->RCGCGPIO |= (1 << 1);
    while ((SYSCTL->PRGPIO & (1 << 1)) == 0)
        ;

    // Configure PB0 (RS), PB1 (EN), PB4–PB7 (data) as output
    GPIOB->DIR |= RS | EN | DATA_MASK;
    GPIOB->DEN |= RS | EN | DATA_MASK;
    GPIOB->DATA &= ~(RS | EN | DATA_MASK);  // Clear all

    SysTick_Init();

    delay_ms(50);  // Wait for LCD to power up

    // Initialization sequence (8-bit interface mode to start)
    LCD_SendNibble(0x03);
    delay_ms(5);

    LCD_SendNibble(0x03);
    delay_us(150);

    LCD_SendNibble(0x03);
    delay_us(150);

    LCD_SendNibble(0x02);  // Set 4-bit mode
    delay_us(150);

    // Now in 4-bit mode: use full commands
    LCD_Command(0x28); // Function set: 4-bit, 2 lines, 5x8 dots
    LCD_Command(0x0C); // Display ON, Cursor OFF
    LCD_Command(0x06); // Entry mode: increment cursor
    LCD_Command(0x01); // Clear display
    delay_ms(2);
}

//====================[ LCD Command/Data API ]====================
void LCD_Command(unsigned char command)
{
    GPIOB->DATA &= ~RS; // RS = 0 for command
    delay_us(1);
    LCD_SendNibble(command >> 4);     // Upper nibble
    LCD_SendNibble(command & 0x0F);   // Lower nibble
    delay_ms(2);
}

void LCD_Data(unsigned char data)
{
    GPIOB->DATA |= RS; // RS = 1 for data
    delay_us(1);
    LCD_SendNibble(data >> 4);
    LCD_SendNibble(data & 0x0F);
    delay_ms(1);
}

void LCD_Clear(void)
{
    LCD_Command(0x01);
    delay_ms(2);
}

void LCD_SetCursor(unsigned char row, unsigned char col)
{
    unsigned char address = (row == 0) ? 0x80 + col : 0xC0 + col;
    LCD_Command(address);
    delay_ms(1);
}

void LCD_Print(char *str)
{
    while (*str)
    {
        LCD_Data(*str++);
    }
}

lcd.h

#ifndef LCD_H
#define LCD_H

#include "TM4C123.h"

// LCD pin definitions (connected to PORTB)
#define RS         (1 << 0)  // PB0
#define EN         (1 << 1)  // PB1
#define DATA_MASK  0xF0      // PB4–PB7

// Function prototypes
void LCD_Init(void);
void LCD_Command(unsigned char cmd);
void LCD_Data(unsigned char data);
void LCD_Clear(void);
void LCD_SetCursor(unsigned char row, unsigned char col);
void LCD_Print(char *str);
void delay_us(int us);
void delay_ms(int ms);

#endif

Lab Work

1. Modify the code

   Update the existing program to display your name on the first line and your ID on the second line of the LCD.

2. Name scrolling with button control

   Write a program that:

   • Displays your name on the LCD.
   • Allows the name to scroll left or right.
   • Uses the two on-board push buttons (with interrupts) to control the scrolling direction.

3. Bidirectional shifting after button press

   Write a program that:

   • Displays your name on the first row and your ID on the second row.
   • The name (first row) continuously shifts right.
   • The ID (second row) continuously shifts left.
   • The shifting starts only after a button press by the user.