Serial LCD Interface I2C

Interfacing LCD Display with serial Interface like I2C can save microcontroller I/O making it a practical alternative to a standard parallel 8 bit interface. We’ll use PCF8574 I2C port expander and PIC16F876A microcontroller to establish IIC communication by 2 lines, SCL – Clock and SDA – Data. The disadvantage of this approach is that required code is a bit more complicated compared to a parallel interface. Here instead of sending 8 bits of command and data we’ll configure an LCD to operate in 4 bit mode and send two 4 bits nibbles. PCF8574 outputs are directly connected to LCD lines in the following way: D5 is R/S, D4 – EN and D3,D2,D1,D0 – Data. See design schematic for more details.

Serial LCD Interface I2C Schematic Parts of the design code were taken and modified from Interfacing HD44780 Character LCD Display and PCF8574 I2C 8-bit I/O expander posts. It’s probably not the most efficient implementation but it does the job of controlling the LCD display. 2×16 LCD module was used however the circuit can be upgraded for other display types. Design prototype board is shown below. Assembly code is available here.
Serial LCD Interface I2C Prototype Board


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