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
To download the code, click DOWNLOAD button and view the Ad. The project will download after the Ad is finished.

40 Comments. Leave new

  • Hi, I used your library and works unstable, some times yes and others not, could be the frecuency of scl?, some clock configuration? I saw there are some options for frecuency output selection in the ioc configuration screen

    • Try using the pull up resistors on the SCL and SDA pins. The baud 100KHz is standard , but you can try 400KHz also. See if it does any improvements

  • Muhammad Hassan
    April 8, 2023 5:22 PM

    is this work for stm32f407 or not?? i changed the #include “stm32f1xx_hal.h” to #include “stm32f4xx_hal.h” but i got nothing on display

  • Hello everyone !
    I tried this tutorial, it’s very useful, thanks !

    I would like to print on my LCD display some values like voltage (using a potentiometer plugged on Analong input).
    Is there any “printf” function in this project ? I can’t find it…

    Thank you very much !

    • convert the data to string using sprintf function
      send the data to lcd using lcd_send_string

      PS: don’t look for arduino reference everywhere. Not every library is written as per arduino terminology.

  • it is a very useful video and tutorial. I use stm32f429zi to generate a pulse for the Triac, so i have a timer output compare that give me the pulse but when i link the lcd display , the display and your code works fine but the pulse misses. The output of timer1 is 3,3 V instead of the pulse. What can i do to resolve? thank you sir

    • That is not related to display. There must be something in the code or the Pins you are selecting. It is highly unlikely that using a display is going top mess up the timer.

      • i have initialize the timer in one pulse mode , in the ch2 i have a square wave input and the ch2 i have the output(pulse for a thyristor)


  • If i am using a keypad, how can i send the pressed bottun only one time to the LCD?
    I use the lcd_send_string function but it keeps writting the number as long as the bottun is pressed.
    I mean so a function: lcd_send_char().

  • I have just found this and am working this example with a F411RE and getting some errors: /Drivers/STM32F4xx_HAL_Driver/Inc/stm32f4xx_hal.h:220:1: error: unknown type name ‘HAL_StatusTypeDef’
    I have replaced your include file in i2c-lcd.h with stm32f4xx_hal_conf.h which solved some errors.
    How can I move forward ?

  • Hi
    Where i found DDRAM pleace. I have got lcd16x4 (LCD-AC-1604A-FHW K/W-E6 C) and when i applaying ur code i saw olny black squares. I try adjust contrast but didn’t help. (Yes i change slave id )

  • sorry.

    The I2C address in i2c-lcd.c most be in the form:#define SLAVE_ADDRESS_LCD (0x3F << 1) // change this according to your setup

    • Why is that ?
      You must be using PCF8574A, so the address for your device is 0x7E.
      I have used PCF8574, so the address is 0x4E

  • Good tutorial with some things to be fixed.
    The I2C address in i2c-lcd.h most be in the form:

    #define SLAVE_ADDRESS_LCD (0x3F << 1) // change this according to your setup

  • how can i send a data with 4 number ?

    • use sprintf to converts the number to characters
      char buf[4];
      sprintf (buf, “%d”, num);
      lcd_send_string (buf);

  • Hi
    this is wrong libraey for i2c lcd 2004

  • I am a beginner of the stm32 boards so could you please given a LCD
    code for stm32f4discovery board

  • Thanks sir, but I do every step as you did successful(build and debug) and I get empty lcd. I have tried address 0x4E and 0x27(it works for arduino and pi), also I increased the delay before initialization and same result?

  • thank you for this great tutorial.
    but I m facing a problem of displaying garbage data on LCD when the MCU is reset. Though I have used i2c module with 20×4 LCD along with bypass caps on Vcc of i2c module, this problem is very frequent and since I have to commercialize my work, I m facing great loss because of this.
    Could u please suggest some software and hardware changes

  • Hi nice post!! do you have a command to turn off the lcd´s light, like a standby mode.

  • You have library i2c-lcd.h i2c-lcd.c ?????


Leave a Reply

Your email address will not be published. Required fields are marked *

Fill out this field
Fill out this field
Please enter a valid email address.


Adblocker detected! Please consider reading this notice.

We've detected that you are using AdBlock Plus or some other adblocking software which is preventing the page from fully loading.

We don't have any banner, Flash, animation, obnoxious sound, or popup ad. We do not implement these annoying types of ads!

We need money to operate the site, and almost all of it comes from our online advertising.

Please add to your ad blocking whitelist or disable your adblocking software.