LCD Programming Example using 'C'

Eight-bit interface using software time delays.

This is a somewhat more flexible version of the basic program.   At the expense of more complicated programming the eight data lines as well as the Enable and Register Select lines may be implemented on any available I/O pin of any port.

The source code is here.
A similar program written in Assembly Language is here.
A similar program written for the Arduino IDE is here.
The list of all LCD programming examples is here.

/**************************************************************************** LCD-AVR-8d.c - Use an HD44780U based LCD with an Atmel ATmega processor Copyright (C) 2013 Donald Weiman ( This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program. If not, see <>. */ /**************************************************************************** File: LCD-AVR-8d.c Date: September 16, 2013 Target: ATmega328 Compiler: avr-gcc (AVR Studio 6) Author: Donald Weiman Summary: 8-bit data interface, busy flag not implemented. Any LCD pin can be connected to any available I/O port. Includes a simple write string routine. */ /******************************* Program Notes ****************************** This program uses an 8-bit data interface but does not use the busy flag to determine when the LCD controller is ready. The LCD RW line (pin 5) is not connected to the uP and it must be connected to GND for the program to function. All time delays are longer than those specified in most datasheets in order to accommodate slower than normal LCD modules. This requirement is well documented but almost always ignored. The information is in a note at the bottom of the right hand (Execution Time) column of the instruction set. *************************************************************************** The eight data lines as well as the two control lines may be implemented on any available I/O pin of any port. These are the connections used for this program: ----------- ---------- | ATmega328 | | LCD | | | | | | PD7|---------------->|D7 | | PD6|---------------->|D6 | | PD5|---------------->|D5 | | PD4|---------------->|D4 | | PD3|---------------->|D3 | | PD2|---------------->|D2 | | PD1|---------------->|D1 | | PD0|---------------->|D0 | | | | | | PB1|---------------->|E | | | GND --->|RW | | PB0|---------------->|RS | ----------- ---------- **************************************************************************/ #define F_CPU 16000000UL #include <avr/io.h> #include <util/delay.h> // LCD interface (should agree with the diagram above) // make sure that the LCD RW pin is connected to GND #define lcd_D7_port PORTD // lcd D7 connection #define lcd_D7_bit PORTD7 #define lcd_D7_ddr DDRD #define lcd_D6_port PORTD // lcd D6 connection #define lcd_D6_bit PORTD6 #define lcd_D6_ddr DDRD #define lcd_D5_port PORTD // lcd D5 connection #define lcd_D5_bit PORTD5 #define lcd_D5_ddr DDRD #define lcd_D4_port PORTD // lcd D4 connection #define lcd_D4_bit PORTD4 #define lcd_D4_ddr DDRD #define lcd_D3_port PORTD // lcd D3 connection #define lcd_D3_bit PORTD3 #define lcd_D3_ddr DDRD #define lcd_D2_port PORTD // lcd D2 connection #define lcd_D2_bit PORTD2 #define lcd_D2_ddr DDRD #define lcd_D1_port PORTD // lcd D1 connection #define lcd_D1_bit PORTD1 #define lcd_D1_ddr DDRD #define lcd_D0_port PORTD // lcd D0 connection #define lcd_D0_bit PORTD0 #define lcd_D0_ddr DDRD #define lcd_E_port PORTB // lcd Enable pin #define lcd_E_bit PORTB1 #define lcd_E_ddr DDRB #define lcd_RS_port PORTB // lcd Register Select pin #define lcd_RS_bit PORTB0 #define lcd_RS_ddr DDRB // LCD module information #define lcd_LineOne 0x00 // start of line 1 #define lcd_LineTwo 0x40 // start of line 2 //#define lcd_LineThree 0x14 // start of line 3 (20x4) //#define lcd_lineFour 0x54 // start of line 4 (20x4) //#define lcd_LineThree 0x10 // start of line 3 (16x4) //#define lcd_lineFour 0x50 // start of line 4 (16x4) // LCD instructions #define lcd_Clear 0b00000001 // replace all characters with ASCII 'space' #define lcd_Home 0b00000010 // return cursor to first position on first line #define lcd_EntryMode 0b00000110 // shift cursor from left to right on read/write #define lcd_DisplayOff 0b00001000 // turn display off #define lcd_DisplayOn 0b00001100 // display on, cursor off, don't blink character #define lcd_FunctionReset 0b00110000 // reset the LCD #define lcd_FunctionSet8bit 0b00111000 // 8-bit data, 2-line display, 5 x 7 font #define lcd_SetCursor 0b10000000 // set cursor position // Program ID uint8_t program_author[] = "Donald Weiman"; uint8_t program_version[] = "LCD-AVR-8d (gcc)"; uint8_t program_date[] = "Sep 16, 2013"; // Function Prototypes void lcd_write_8(uint8_t); void lcd_write_instruction_8d(uint8_t); void lcd_write_character_8d(uint8_t); void lcd_write_string_8d(uint8_t *); void lcd_init_8d(void); /******************************* Main Program Code *************************/ int main(void) { // configure the microprocessor pins for the data lines lcd_D7_ddr |= (1<<lcd_D7_bit); // 8 data lines - output lcd_D6_ddr |= (1<<lcd_D6_bit); lcd_D5_ddr |= (1<<lcd_D5_bit); lcd_D4_ddr |= (1<<lcd_D4_bit); lcd_D3_ddr |= (1<<lcd_D3_bit); lcd_D2_ddr |= (1<<lcd_D2_bit); lcd_D1_ddr |= (1<<lcd_D1_bit); lcd_D0_ddr |= (1<<lcd_D0_bit); // configure the microprocessor pins for the control lines lcd_E_ddr |= (1<<lcd_E_bit); // E line - output lcd_RS_ddr |= (1<<lcd_RS_bit); // RS line - output // initialize the LCD controller as determined by the defines (LCD instructions) lcd_init_8d(); // initialize the LCD display for an 8-bit interface // display the first line of information lcd_write_string_8d(program_author); // set cursor to start of second line lcd_write_instruction_8d(lcd_SetCursor | lcd_LineTwo); _delay_us(80); // 40 uS delay (min) // display the second line of information lcd_write_string_8d(program_version); // endless loop while(1); return 0; } /******************************* End of Main Program Code ******************/ /*============================== 8-bit LCD Functions ======================*/ /* Name: lcd_init_8d Purpose: initialize the LCD module for a 8-bit data interface Entry: equates (LCD instructions) set up for the desired operation Exit: no parameters Notes: uses time delays rather than checking the busy flag */ void lcd_init_8d(void) { // Power-up delay _delay_ms(100); // initial 40 mSec delay // Reset the LCD controller lcd_write_instruction_8d(lcd_FunctionReset); // first part of reset sequence _delay_ms(10); // 4.1 mS delay (min) lcd_write_instruction_8d(lcd_FunctionReset); // second part of reset sequence _delay_us(200); // 100uS delay (min) lcd_write_instruction_8d(lcd_FunctionReset); // third part of reset sequence _delay_us(200); // this delay is omitted in the data sheet // Function Set instruction lcd_write_instruction_8d(lcd_FunctionSet8bit); // set mode, lines, and font _delay_us(80); // 40uS delay (min) // The next three instructions are specified in the data sheet as part of the initialization routine, // so it is a good idea (but probably not necessary) to do them just as specified and then redo them // later if the application requires a different configuration. // Display On/Off Control instruction lcd_write_instruction_8d(lcd_DisplayOff); // turn display OFF _delay_us(80); // 40 uS delay (min) // Clear Display instruction lcd_write_instruction_8d(lcd_Clear); // clear display RAM _delay_ms(4); // 1.64 mS delay (min) // ; Entry Mode Set instruction lcd_write_instruction_8d(lcd_EntryMode); // set desired shift characteristics _delay_us(80); // 40 uS delay (min) // This is the end of the LCD controller initialization as specified in the data sheet, but the display // has been left in the OFF condition. This is a good time to turn the display back ON. // Display On/Off Control instruction lcd_write_instruction_8d(lcd_DisplayOn); // turn the display ON _delay_us(80); // 40 uS delay (min) } /*........................................................................... Name: lcd_write_string_8d ; Purpose: display a string of characters on the LCD Entry: (theString) is the string to be displayed Exit: no parameters Notes: uses time delays rather than checking the busy flag */ void lcd_write_string_8d(uint8_t theString[]) { volatile int i = 0; // character counter*/ while (theString[i] != 0) { lcd_write_character_8d(theString[i]); i++; _delay_us(80); // 40 uS delay (min) } } /*........................................................................... Name: lcd_write_character_8d Purpose: send a byte of information to the LCD data register Entry: (theData) is the information to be sent to the data register Exit: no parameters Notes: does not deal with RW (busy flag is not implemented) */ void lcd_write_character_8d(uint8_t theData) { lcd_RS_port |= (1<<lcd_RS_bit); // select the Data Register (RS high) lcd_E_port &= ~(1<<lcd_E_bit); // make sure E is initially low lcd_write_8(theData); // write the data } /*........................................................................... Name: lcd_write_instruction_8d Purpose: send a byte of information to the LCD instruction register Entry: (theInstruction) is the information to be sent to the instruction register Exit: no parameters Notes: does not deal with RW (busy flag is not implemented) */ void lcd_write_instruction_8d(uint8_t theInstruction) { lcd_RS_port &= ~(1<<lcd_RS_bit); // select the Instruction Register (RS low) lcd_E_port &= ~(1<<lcd_E_bit); // make sure E is initially low lcd_write_8(theInstruction); // write the instruction } /*........................................................................... Name: lcd_write_8 Purpose: send a byte of information to the LCD module Entry: (theByte) is the information to be sent to the desired LCD register RS is configured for the desired LCD register E is low RW is low Exit: no parameters Notes: use either time delays or the busy flag */ void lcd_write_8(uint8_t theByte) { lcd_D7_port &= ~(1<<lcd_D7_bit); // assume that data is '0' if (theByte & 1<<7) lcd_D7_port |= (1<<lcd_D7_bit); // make data = '1' if necessary lcd_D6_port &= ~(1<<lcd_D6_bit); // repeat for each data bit if (theByte & 1<<6) lcd_D6_port |= (1<<lcd_D6_bit); lcd_D5_port &= ~(1<<lcd_D5_bit); if (theByte & 1<<5) lcd_D5_port |= (1<<lcd_D5_bit); lcd_D4_port &= ~(1<<lcd_D4_bit); if (theByte & 1<<4) lcd_D4_port |= (1<<lcd_D4_bit); lcd_D3_port &= ~(1<<lcd_D3_bit); if (theByte & 1<<3) lcd_D3_port |= (1<<lcd_D3_bit); lcd_D2_port &= ~(1<<lcd_D2_bit); if (theByte & 1<<2) lcd_D2_port |= (1<<lcd_D2_bit); lcd_D1_port &= ~(1<<lcd_D1_bit); if (theByte & 1<<1) lcd_D1_port |= (1<<lcd_D1_bit); lcd_D0_port &= ~(1<<lcd_D0_bit); if (theByte & 1<<0) lcd_D0_port |= (1<<lcd_D0_bit); // write the data // 'Address set-up time' (40 nS) lcd_E_port |= (1<<lcd_E_bit); // Enable pin high _delay_us(1); // implement 'Data set-up time' (80 nS) and 'Enable pulse width' (230 nS) lcd_E_port &= ~(1<<lcd_E_bit); // Enable pin low _delay_us(1); // implement 'Data hold time' (10 nS) and 'Enable cycle time' (500 nS) }