STM32 I²C LCD

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16x2 LCD Module

LCD Display modules are readily available and they are dirt cheap (< $2 typically). They come in different "resolutions" typically expressed as number of characters and number of lines. Common ones are 1602 (16 characters in 2 lines) and 2004 (20 characters in 4 lines).

The modules are interfaces by an 8 bit parallel data bus (can be operated in 4 bit mode) and some control signals:

116X2-LCD-Pinouts.png

These can of course be "driven" by an STM32 by interfacing these pins directly, but at a minimum that would tie up 8 GPIO pins for one display.

To cut down on the number of pins needed a GPIO extender can be used and because this approach is quite a lot easier a lot of the LCD modules come with an I²C GPIO extender already attached.

I2C extender on LCD display.webp

The I²C extender is connected in the following way:

I2c Module to LCD.png

In other words, the 8 bits of the GPIO extender is mapped as follows:

Name Function Description
P7 D7 MSB of data
P6 D6
P5 D5
P4 D4
P3 BT Backlight control
P2 E Enable pin
P1 RW Read/write toggle
P0 RS

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