Lab 10: LCD Interfacing (16x2) - 8-bit Mode

Learn LCD display control using parallel communication. Display text, numbers, and create interactive menus on a 16x2 character LCD.

Learning Objectives

By the end of this lab, you will:

• 🎯 Understand HD44780 LCD controller operation
• 🎯 Master 8-bit parallel communication protocol
• 🎯 Implement LCD initialization sequence
• 🎯 Write text to LCD display
• 🎯 Create dynamic display content

Prerequisites

• ✅ Complete Labs 1-9 (GPIO, timing, interrupts)
• ✅ Understand parallel communication basics
• ✅ Familiar with command vs data concepts

Hardware Required

Component	Details
Microcontroller	STM32F407VG
LCD Display	16x2 HD44780 compatible
8 Data Lines	GPIO PD2-PD9 (or D0-D7)
Control Lines	RS (PD0), EN (PD1), RW (GND)
Power	5V for LCD, 0.1µF caps on power
Contrast	10K potentiometer on contrast pin

Theory: LCD Communication

HD44780 Protocol

LCD needs 3 signals:
  ├─ RS (Register Select):
  │  ├─ 0 = Command register (instructions)
  │  └─ 1 = Data register (characters)
  │
  ├─ EN (Enable):
  │  ├─ Pulse HIGH then LOW to latch data
  │  └─ Data valid on HIGH->LOW transition
  │
  └─ RW (Read/Write):
     ├─ 0 = Write (we'll tie to GND)
     └─ 1 = Read (not used in this lab)

8-bit Data Transfer

Data lines D0-D7 on GPIO pins
Each data byte represents either:
  ├─ Command (RS=0): e.g., 0x01 = Clear
  └─ Data (RS=1): e.g., ASCII 'A' = 0x41

Timing:
  1. Set RS for command or data
  2. Place 8-bit data on D0-D7
  3. Pulse EN: HIGH for 1µs, then LOW
  4. Wait for LCD to process (40µs typical)

Common Commands

0x01  Clear display
0x02  Return cursor to home
0x38  Function set: 8-bit, 2 lines, 5x8 font
0x0C  Display ON, cursor OFF, no blink
0x06  Entry mode: increment cursor, no shift
0x80  Cursor position: line 1, character 1
0xC0  Cursor position: line 2, character 1

Complete Code

#define RCC_AHB1ENR *(volatile unsigned int*)(0x40023800 + 0x30)
#define GPIOD_MODER *(volatile unsigned int*)(0x40020C00 + 0x00)
#define GPIOD_ODR   *(volatile unsigned int*)(0x40020C00 + 0x14)

#define RS (1<<0)
#define EN (1<<1)

void delay_ms(int ms) {
    for (volatile int i = 0; i < ms * 5000; i++);
}

void lcd_enable(void) {
    GPIOD_ODR |= EN;
    delay_ms(1);
    GPIOD_ODR &= ~EN;
}

void lcd_send(unsigned char byte, int is_data) {
    if (is_data)
        GPIOD_ODR |= RS;     // Data mode
    else
        GPIOD_ODR &= ~RS;    // Command mode
    
    // Place byte on D0-D7
    GPIOD_ODR &= ~(0xFF << 2);  // Clear bits
    GPIOD_ODR |= (byte << 2);   // Set data bits
    
    lcd_enable();
    delay_ms(2);
}

void lcd_init(void) {
    RCC_AHB1ENR |= (1 << 3);  // Enable GPIOD
    
    // Configure PD0-PD9 as outputs
    GPIOD_MODER &= ~(0xFFFFF);
    GPIOD_MODER |= (0x55555);
    
    delay_ms(50);
    
    // Initialization sequence
    lcd_send(0x38, 0);  // 8-bit mode, 2 lines
    delay_ms(5);
    lcd_send(0x0C, 0);  // Display ON
    delay_ms(2);
    lcd_send(0x01, 0);  // Clear display
    delay_ms(2);
    lcd_send(0x06, 0);  // Cursor increment
}

void lcd_cmd(unsigned char cmd) {
    lcd_send(cmd, 0);
}

void lcd_char(unsigned char ch) {
    lcd_send(ch, 1);
}

void lcd_string(char *str) {
    while (*str) {
        lcd_char(*str++);
    }
}

void lcd_goto_line2(void) {
    lcd_cmd(0xC0);  // Line 2, position 0
}

int main(void) {
    lcd_init();
    
    lcd_string("STM32 LCD");
    lcd_goto_line2();
    lcd_string("Hello!");
    
    while (1) {
        // Application
    }
    
    return 0;
}

Expected Output

LCD Screen:
┌─────────────────┐
│ STM32 LCD       │
│ Hello!          │
└─────────────────┘

Initialization Flow

Power up
  ↓
Wait 15ms+ for LCD stable
  ↓
Send 0x38 (8-bit, 2 line, 5x8 font)
  ↓
Send 0x0C (display ON, cursor OFF)
  ↓
Send 0x01 (clear screen)
  ↓
Send 0x06 (entry mode)
  ↓
Ready for data

Common Mistakes

Issue	Solution
LCD always blank	Check power, contrast, RS/EN wiring
Garbled text	Verify 8-bit alignment - must be bits [9:2]
No response	Ensure EN pulses correctly
Character corruption	Check timing - may need longer delays

Key Takeaways

✨ Important:

1. RS pin selects command vs data register
2. EN pulse latches data into LCD
3. Initialization sequence is specific
4. 8-bit mode uses 8 parallel data lines
5. Timing must account for LCD processing

Challenge Exercises

Challenge 1: Display Counter

Show a number that increments every second.

Challenge 2: Button-Controlled Menu

Display menu items, navigate with buttons.

Challenge 3: Sensor Display

Show real-time temperature or other sensor values.

Next Steps

✨ Congratulations! You've completed a comprehensive STM32 embedded systems course!

Review of Mastered Topics:

• ✅ GPIO output and input control
• ✅ Bitwise operations and bit manipulation
• ✅ Software debouncing techniques
• ✅ Binary number representation
• ✅ Audio output and tone generation
• ✅ Hardware timers and exact timing
• ✅ External interrupts and event handling
• ✅ Parallel LCD interfacing

Future Learning Paths:

1. Advanced: PWM, ADC, DAC, SPI, I2C, UART
2. Real-time OS: FreeRTOS on STM32
3. HAL/Cube: High-level abstractions for faster development
4. Advanced Interrupts: Nested vectored interrupt controller (NVIC)
5. Real-world Projects: Build IoT, automation, sensor systems