Interfacing I2C LCD with PIC microcontroller | MPLAB Projects

Interfacing LCD display with a PIC microcontroller requires at least 6 data pins (for LCD pins: RS, E, D4, D5, D6 and D7). Number of pins needed for the LCD can be reduced to 2 by using an I2C I/O (Input/Output) expander like PCF8574 or PCF8574A. Adding the I2C I/O expander builds an I2C LCD. The I2C LCD is connected with the microcontroller via 2 lines: SDA (serial data) and SCL (serial clock). I2C = IIC = Inter-Integrated Circuit.

This post shows an example for connecting LCDs (with HD44780 or complaint controller) with Microchip PIC12F1822 8-bit microcontroller, this microcontroller has only 8 pins of which 5 can be used as outputs, therefore an I2C LCD is required.
This project works also with DFRobot I2C LCD displays.

The compiler used in this project is Microchip MPLAB XC8 (MPLAB X IDE with MPLAB XC8 compiler). An I2C LCD driver for the MPLAB XC8 compiler is required to simplify example C code. This driver is just a C file named (with extension) I2C_LCD.c, we’ve to add this file to project folder, download link is below:
I2C LCD driver for MPLAB XC8 compiler

Related Project:
Interfacing LCD with PIC microcontroller | MPLAB Projects

Hardware Required:
The components listed below are required for this project.

  • PIC12F1822 microcontroller  —  datasheet
  • LCD screen (16×2, 20×4 …)
  • PCF8574 I/O expander (or PCF8574A)   —   PCF8574 datasheet
  • 5 x 10k ohm resistor
  • 330 ohm resistor
  • 10k ohm variable resistor or potentiometer
  • 5V source
  • Breadboard
  • Jumper wires

PIC12F1822 MCU with I2C LCD circuit

Interfacing I2C LCD with PIC microcontroller circuit:
Project circuit schematic diagram is shown below.

PIC12F1822 I2C LCD circuit with PCF8574

(All grounded terminals are connected together)

The PIC12F1822 microcontroller has one hardware I2C module with SDA on pin RA2 (#5) and SCL on pin RA1 (#6). SDA and SCL pins of the PIC12F1822 MCU are connected to SDA (#15) and SCL (#14) pins of the PCF8574 I/O expander respectively.

A2, A1 and A0 pins of the PCF8574 are connected to +5V (each one through 10k resistor) which means the I2C address of the PCF8574 (therefor the I2C LCD) is: 0 1 0 0 A2 A1 A0 0 = 0 1 0 0 1 1 1 0 = 0x4E. The 10k ohm resistors for A2, A1 and A0 are optional and each pin can be connected directly to +5V.

PCF8574A can be used instead of the PCF8574, the I2C address becomes: 0x7E.

In this project the PIC12F1822 microcontroller runs with its internal oscillator @ 8 MHz, MCLR pin is configured as an input pin.

Interfacing I2C LCD with PIC microcontroller C code:
The C code below is for MPLAB XC8 compiler, it was tested with version 2.00 installed on MPLAB X IDE version 5.05.

The I2C LCD driver file is included with the line:
#include “I2C_LCD.c”

The hardware I2C module of the PIC12F1822 is initialized with a clock frequency of 100KHz (100000Hz):
I2C_Init(100000);

The I2C LCD is initialized with an I2C address of 0x4E:
LCD_Begin(0x4E);

The microcontroller used in this example is PIC12F1822, configuration words are:

Where:

  • Fail-Safe Clock Monitor enabled
  • Internal/External Switchover mode enabled
  • CLKOUT function is disabled, I/O function on the CLKOUT pin
  • Brown-out Reset (BOR) enabled
  • Data memory code protection disabled
  • Program memory code protection disabled
  • RE3/MCLR pin function is digital input, MCLR internally tied to VDD
  • Power-up Timer (PWRT) disabled
  • Watchdog Timer (WDT) disabled
  • INTOSCIO oscillator: I/O function on CLKIN pin
  • Low voltage programming disabled
  • In-Circuit Debugger disabled
  • Brown-out Reset voltage (Vbor), low trip point selected
  • Stack Overflow or Underflow will cause a Reset
  • 4xPLL disabled
  • Flash Program Memory Self Write disabled

MPLAB XC8 code:

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