This project will cover the configuration and implementation of a universal LCD display interface with an STM32 microcontroller using the standard 4-bit communication protocol (HD44780). The primary goal is to create a flexible driver capable of controlling various display sizes—including 16x2, 20x4, and 8x1—from a single codebase.
The 4-bit Communication Mode reduces the number of required GPIO pins from 11 to 6 by sending data in two, 4-bit nibbles (high nibble first, then low nibble). This method efficiently utilizes microcontroller resources while maintaining full display functionality. The STM32's 3.3V logic high level is successfully recognized by the 5V LCD's input pins, which typically have a minimum "VIH" (Input High Voltage) threshold of around 2.0V, making the 3.3V signal valid.
STM32CubeMX Configuration- Create a new STM32F103C6 project.
- Set the system clock to 8 MHz (HSI).
- GPIO Configuration: Configure the following pins as GPIO Output:
- RS (Register Select): PB3
- EN (Enable): PB4
- D4: PB5
- D5: PB6
- D6: PB7
- D7: PB8
- Generate the initialization code.
- Open the generated project.
- In the Core/Src folder, create custom driver files: LiquidCrystal.h and LiquidCrystal.c.
- Implement the core functions in the driver:
- LCD_Init(): Sequences the LCD startup and sets 4-bit mode.
- LCD_SendCmd(uint8_t cmd): Sends a command byte to the LCD.
- LCD_SendData(uint8_t data): Sends a character byte to the LCD.
- LCD_SendString(char *str): Sends a full null-terminated string to be displayed.
- Include
LiquidCrystal.hinmain.cand write the application logic to initialize the LCD and display messages.
Build the project. - Build the project.
- Add an STM32F103C6 and a LM016L (16x2 LCD) to the schematic.
- Wiring:
- Connect STM32 pins PB3-PB8 to the corresponding LCD pins (RS, EN, D4-D7).
- Connect the LCD's VDD pin to the 5V power rail.
- Connect the LCD's VSS and VEE (contrast) pins to ground through a potentiometer.
- Load the compiled .hex file into the MCU.
- Start the simulation to test the display output. The 3.3V signals from the STM32 will correctly drive the 5V LCD.
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