C Library for LCD 1602 with expander I2C

Library used I/O expander PCF8574 to control 1602 LCD display with HD44780 driver via I2C communication protocol. Main aim is reduce number of hardware connection and safe pins of microcontroller.

HD44780 Description

Detailed information is in HD44780 Datasheet.

PCF8574 Description

Detailed information is in PCF8574 Datasheet.

Hardware connection

PCF8574 PIN	ATMEGA328 PIN	ARDUINO UNO PIN	Description
UCC	+5V	+5V	Supply Voltage
USS	GND	GND	Ground
SDA	PC4	A4	Data
SCL	PC5	A5	Clock

Library

Library is aimed for MCU ATmega328 / Atmega8 which supports 4-bit Operation.

Tested

Library was tested and proved on a 16x2 LCD Display with Atmega328p.

Usage

Prior defined for:

• Atmega328p / Atmega8
• LCD 16x2

Initializing 4-bit operation

Initializing LCD Driver HD44780 according to Figure 24 in HD44780 Datasheet.

// +---------------------------+
// |         Power on          |
// | Wait for more than 15 ms  |   // 15 ms wait
// | after VCC rises to 4.5 V  |
// +---------------------------+
//              |
// +---------------------------+ 
// |  RS R/W DB7 DB6 DB5 DB4   |
// |   0   0   0   0   1   1   |   // Initial sequence 0x30
// | Wait for more than 4.1 ms |   // 4.1 ms us writing DATA into DDRAM or CGRAM
// +---------------------------+
//              |
// +---------------------------+
// |  RS R/W DB7 DB6 DB5 DB4   |
// |   0   0   0   0   1   1   |   // Initial sequence 0x30
// | Wait for more than 0.1 ms |   // 100 us writing DATA into DDRAM or CGRAM
// +---------------------------+
//              |
// +---------------------------+   // Initial sequence 0x30
// |  RS R/W DB7 DB6 DB5 DB4   |   // 37 us writing DATA into DDRAM or CGRAM
// |   0   0   0   0   1   1   |   // 4us tadd - time after BF disapeared
// | Wait for more than 45 us  |   // 37 us + 4 us = 41 us * (270/250) = 45us
// +---------------------------+
//              |
// +---------------------------+   // 4bit mode 0x20
// |  RS R/W DB7 DB6 DB5 DB4   |   // 37 us writing DATA into DDRAM or CGRAM
// |   0   0   0   0   1   0   |   // 4us tadd - time after BF disapeared
// | Wait for more than 45 us  |   // !!! BUSY FLAG CHECK DOESN'T WORK CORRECTLY !!!
// +---------------------------+
//              |
// +---------------------------+
// |  RS R/W DB7 DB6 DB5 DB4   |   // Display off 0x08
// |   0   0   0   0   0   0   |   // 
// |   0   0   1   0   0   0   |   // 
// |    Wait for BF Cleared    |   // Wait for 50us
// +---------------------------+
//              |
// +---------------------------+
// |  RS R/W DB7 DB6 DB5 DB4   |   // Display clear 0x01
// |   0   0   0   0   0   0   |   //
// |   0   0   0   0   0   1   |   //
// |    Wait for BF Cleared    |   // Wait for 50us
// +---------------------------+
//              |
// +---------------------------+
// |  RS R/W DB7 DB6 DB5 DB4   |   // Entry mode set 0x06
// |   0   0   0   0   0   0   |   // 
// |   0   0   0   1   1   0   |   // shift cursor to the left, without text shifting
// |    Wait for BF Cleared    |   // Wait for 50us
// +---------------------------+

Functions

• HD44780_PCF8574_Init() - init display
• HD44780_PCF8574_DisplayClear() - clear display and set position to 0, 0
• HD44780_PCF8574_DisplayOn() - turn on display
• HD44780_PCF8574_CursorOn() - turn on cursor
• HD44780_PCF8574_CursorBlink() - blink the cursor blink
• HD44780_PCF8574_DrawChar(char) - draw character on display
• HD44780_PCF8574_DrawString(char *) - draw string
• HD44780_PCF8574_PositionXY(char, char) - set position X, Y
• HD44780_PCF8574_Shift(char, char) - shift cursor or display to left or right

HD44780_PCF8574_Init

void HD44780_PCF8574_Init (void)

Base initialisation function. If the electrical characteristics conditions listed under the table Power Supply Conditions Using Internal Reset Circuit are not met, the internal reset circuit will not operate normally and will fail to initialize the HD44780U. For such a case, initialization must be performed by the MPU as explained in the section 4-bit Operation or 8-bit Operation depending on mode.

HD44780_PCF8574_DisplayClear

void HD44780_PCF8574_DisplayClear (void)

Display clear and set cursor to position 0, 0.

HD44780_PCF8574_DisplayOn

void HD44780_PCF8574_DisplayOn (void)

Turn on the display.

HD44780_PCF8574_CursorOn

void HD44780_PCF8574_CursorOn (void)

Turn on the cursor and display on. Cursor will be visible. IMPORTANT: Function HD44780_CursorOn() besides the cursor on, switch the display on, so don't need to use function HD44780_DisplayOn(). But without function HD44780_CursorOn() display is switched on by the function HD44780_DisplayOn().

HD44780_PCF8574_CursorBlink

void HD44780_PCF8574_CursorBlink (void)

Turn the cursor blink. Cursor will be visible and it will blink. IMPORTANT: Function HD44780_CursorBlink() besides the cursor blink, switch the display on, so don't need to use function HD44780_DisplayOn(). But without function HD44780_CursorBlink() display is switched on by the function HD44780_DisplayOn().

HD44780_PCF8574_DrawChar

void HD44780_PCF8574_DrawChar (char character)

Draw specific char on display according to ASCII table.

HD44780_PCF8574_DrawString

void HD44780_PCF8574_DrawString (char *str)

Draw string.

HD44780_PCF8574_PositionXY

char HD44780_PCF8574_PositionXY (char x, char y)

Set DDRAM or CGRAM at the specific position X, Y. For LCD 16x2 (cols, rows) maximal possible values:

• X from interval values {0; 1; ... 15},
• Y from interval values {0; 1}.

HD44780_PCF8574_Shift

char HD44780_PCF8574_Shift (char item, char direction)

Shift cursor or display to left or right. Item defines either cursor or display we want to move. Two possible values for item are defined:

• HD44780_CURSOR,
• HD44780_DISPLAY.

The second parameter is direction definition. Two possible values for direction are defined:

• HD44780_RIGHT,
• HD44780_LEFT.

Demonstration

Links

• HD44780 Datasheet
• PCF8574 Datasheet NXP
• PCF8574 Datasheet TI