LCD 20X4 using I2C with STM32

In this tutorial we are going to interface LCD 20×4 Display with STM32 using I2C. I am using STM32F103C8 microcontroller and I2C device is PCF8574 with the slave address of 0x4E.

You can use the same code for any other LCD display Type (i.e 16×2, 16X4 etc), except the DDRAM addresses. You can google the addresses for your LCD Type.


Do not use the address 0x27 and 0x35. This is not arduino and these are not the addresses for your device

Arduino (IDE only… not the mcu) uses 7 bit addressing system and the rest (including STM32) uses 8 bits. Whenever you are using the I2C address, use the full 8 bits for the address. You can find the address for your device in it’s datasheet. The address will (mostly) be either 0x4E for PCF8574, or 0x7E for PCF8574A


Working with these LCD displays is pretty simple. All we need to do is the following :-

  • Initialize the display
  • Write the address of the DDRAM
  • Write the character to be displayed


According to the datasheet, To initialize the 20×4 LCD we need to send some sequence of commands to the display. They are as follows:-

Wait for > 45 ms

HAL_Delay(50);  // wait for >40ms

lcd_send_cmd (0x30);
HAL_Delay(5);  // wait for >4.1ms
lcd_send_cmd (0x30);
HAL_Delay(1);  // wait for >100us
lcd_send_cmd (0x30);
lcd_send_cmd (0x20);  // 4bit mode
  • Send the function set instruction with the command (0x30) 3 times
  • The delay between each command varies as shown above.
  • This entire process is than followed by another function set command (0x20)

lcd_send_cmd (0x28); // Function set --> DL=0 (4 bit mode), N = 1 (2 line display) F = 0 (5x8 characters)

Send the function set command (0x28) to set the display in 4 bit mode (DL=0), 2 line display (N=1) and 5×8 fonts (F=0)

lcd_send_cmd (0x08); //Display on/off control --> D=0,C=0, B=0  ---> display off
  • Send the command to the Display On/OFF Control
  • Display off (D=0), Cursor off (C=0) and Blink OFF (B=0)

lcd_send_cmd (0x01);  // clear display

Clear the Display by Sending 0x01.

lcd_send_cmd (0x06); //Entry mode set --> I/D = 1 (increment cursor) & S = 0 (no shift)

Set the entry mode of your choice. I am setting Cursor move as increment (I/D=1) and display shift as OFF (S=0)

lcd_send_cmd (0x0C); //Display on/off control --> D = 1, C and B = 0. (Cursor and blink, last two bits)

Turn the display ON (D=1) along with the choice for cursor and blinking. I am setting both to 0 (C=0, B=0)


Addresses for the DDRAM of the LCD 20×4 is shown below.

While setting an address we need to OR (|) it with the 0x80. For eg if I want to set the cursor to 2nd row, I have to set the address as (0x80|0x40).

If you want to use a 16×4 LCD than the addresses for the DDRAM are shown below. Use the same code with just the change in address.


Check out the Video Below


You can help with the development by DONATING OR Just click DOWNLOAD to download the code

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