hd44780_lcd.c

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/******************************************************************************
 @copyright Copyright © 2022 by Jason Duffy.
 
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/**
 * @file hd44780_lcd.c
 * @ingroup hd44780_lcd
 * @author Jason Duffy
 * @date 1st March 2022
 * @brief Driver for the HD44780 based 16x2 liquid crystal display.
 * @bug No known bugs. 
 * 
 * This file provides the basic low-level functionality for the ubiquitous 16x2
 * display. Please note that it uses long blocking waits in the initialisation
 * routine (100ms), and short blockign waits in other utility functions
 * (2uS - 2mS). This was done to simplify the code as the busy flag read
 * introduced pitfalls. This driver currently only allows for a single display
 * to be used, but this might be improved on at a later date.
 * 
 * NOTE: Values used in bitwise operations MUST be of unsigned type.
 * 
 * This driver was written using the datasheet for the HITACHI HD44780U LCD
 * driver chip, which can be found here:
 * @see http://www.datasheet-pdf.com/PDF/HD44780U-Datasheet-Hitachi-1109874
 */
 
// System utility headers. These are installed along with AVR Crosspack.
#include <avr/io.h>
#include <util/delay.h>
 
//Project specific headers.
#include "hd44780_lcd.h"
#include "pin_defines.h" // Pinout for the display is defined here.
 
/**
 * Local copy of lcd_config_t pointer to store address of config object.
 */
static lcd_config_t *p_config_local;
 
/**
 * Bitmask used to manipulate data based on data length setting in config.
 */
static uint8_t data_length_bitmask = 0;
 
// Base commands without flags applied.
#define CLEAR_DISPLAY               0b00000001U
#define CURSOR_HOME                 0b00000010U
#define ENTRY_MODE_SET              0b00000100U
#define ON_OFF_CTRL                 0b00001000U
#define CURSOR_DISPLAY_SHIFT        0b00010000U
#define FUNCTION_SET                0b00100000U
 
// Bit positions for setting flags in base commands.
#define DATA_LENGTH_BIT             4U
#define DISPLAY_LINES_BIT           3U
#define FONT_SIZE_BIT               2U
#define MOVE_DIRECTION_BIT          1U
#define DISPLAY_SHIFT_BIT           0U
#define CURSOR_ENABLE_BIT           1U
#define BLINK_ENABLE_BIT            0U
#define ON_OFF_CTRL_BIT             2U
#define RIGHT_LEFT_BIT              2U
#define SHIFT_OR_CURSOR_BIT         3U
#define BUSY_FLAG_BIT               7U // Not currently used in this program.
 
// Flags for setting ON_OFF_CTRL_BIT.
#define DISPLAY_ON                  true
#define DISPLAY_OFF                 false
 
// Delay time definitions.
#define POWER_RAMP_DELAY_MS         100
#define SHORT_INSTR_DELAY_MS        2
#define LONG_INSTR_DELAY_MS         10
#define SCROLL_DELAY_MS             400
#define ENABLE_DELAY_US             2
 
// Forward declarations
void lcd_command(uint8_t data);
void lcd_char(char character);
void pulse_enable(void);
 
 
/*
 * Initialisation routine (run once at startup).
 */
void init_lcd(lcd_config_t *p_config)
{
    // copy address of config object pointer to a local pointer
    p_config_local = p_config;
 
    // Set data direction registers to output where applicable
    LCD_CTRL_DDR |= (1U << LCD_RS) | (1U << LCD_EN);
 
    // Test for bit mode and set appropriate bitmask
    if (p_config_local->eight_bit_mode)
    {
        data_length_bitmask = 0xff; // 0b11111111
    }
    else
    {
        data_length_bitmask |= (1U << LCD_D7) | (1U << LCD_D6);
        data_length_bitmask |= (1U << LCD_D5) | (1U << LCD_D4);
    }
 
    // Set relevant lcd data port direction to output
    LCD_DATA_DDR |= data_length_bitmask;
 
    // Delay to allow power ramp up in LCD controller
    _delay_ms(POWER_RAMP_DELAY_MS);
 
    // Begin initialising HD44780
    uint8_t byte = 0;
    byte |= FUNCTION_SET;
    byte |= (p_config_local->eight_bit_mode << DATA_LENGTH_BIT);
 
    for (uint8_t count = 0; count < 3; ++count)
    {
        lcd_command(byte);
        _delay_ms(LONG_INSTR_DELAY_MS);
    }
 
    byte = 0;
    byte |= FUNCTION_SET;
    byte |= (p_config_local->eight_bit_mode << DATA_LENGTH_BIT);
    byte |= (p_config_local->two_line_display << DISPLAY_LINES_BIT);
    byte |= (p_config_local->five_by_ten_font << FONT_SIZE_BIT);
    lcd_command(byte);
 
    byte = 0;
    byte |= ON_OFF_CTRL;
    byte |= (DISPLAY_OFF << ON_OFF_CTRL_BIT);
    byte |= (p_config_local->cursor_enable << CURSOR_ENABLE_BIT);
    byte |= (p_config_local->blink_enable << BLINK_ENABLE_BIT);
    lcd_command(byte);
 
    byte = 0;
    byte |= CLEAR_DISPLAY;
    lcd_command(byte);
 
    byte = 0;
    byte |= ENTRY_MODE_SET;
    byte |= (p_config_local->increment_counter << MOVE_DIRECTION_BIT);
    byte |= (p_config_local->display_shift << DISPLAY_SHIFT_BIT);
    lcd_command(byte);
 
    byte = 0;
    byte |= ON_OFF_CTRL;
    byte |= (DISPLAY_ON << ON_OFF_CTRL_BIT);
    byte |= (p_config_local->cursor_enable << CURSOR_ENABLE_BIT);
    byte |= (p_config_local->blink_enable << BLINK_ENABLE_BIT);
    lcd_command(byte);
    lcd_return_home();
}
 
 
/*
 * Turn display off (config settings are retained).
 */
void lcd_display_off(void)
{
    uint8_t byte = 0;
    byte |= ON_OFF_CTRL; // Default is off
    byte |= (p_config_local->cursor_enable << CURSOR_ENABLE_BIT);
    byte |= (p_config_local->blink_enable << BLINK_ENABLE_BIT);
    lcd_command(byte);
}
 
 
/*
 * Turn display on.
 */
void lcd_display_on(void)
{
    uint8_t byte = 0;
    byte |= ON_OFF_CTRL;
    byte |= (DISPLAY_ON << ON_OFF_CTRL_BIT);
    byte |= (p_config_local->cursor_enable << CURSOR_ENABLE_BIT);
    byte |= (p_config_local->blink_enable << BLINK_ENABLE_BIT);
    lcd_command(byte);
}
 
 
/*
 * Prints a string of characters to the display.
 */
void lcd_print_string(const char *str)
{
    for (uint8_t index = 0; str[index] != 0; ++index)
    {
        lcd_char(str[index]);
    }
}
 
 
/*
 * Prints an integer variable.
 */
void lcd_print_integer(int16_t number)
{
    if (number < 0)
    {
        lcd_char('-');
    }
 
    uint8_t count = 0;
    uint8_t digit = 0;
    char str[20];
 
    while (number > 0)
    {
        digit = number % 10;
        str[count] = (digit + '0');
        ++count;
        number /= 10;
    }
 
    while (count > 0)
    {
        lcd_char(str[count - 1]);
        --count;
    }
}
 
 
/*
 * Sets cursor location using x and y coordinates.
 */ 
void lcd_set_cursor(uint8_t column, uint8_t row)
{
    uint8_t address = 0;
 
    if (row == 0)
    {
        address = column;
    }
 
    else if (row == 1)
    {
        address = (column + 64);
    }
 
    address |= 0x80U; // Write 1 to MSB
    lcd_command(address);
}
 
 
/*
 * Writes space characters to all 32 sections of display (or 16 if in 1 line
 * mode).
 */
void lcd_fast_clear(void)
{
    lcd_set_cursor(0,0);
    for (uint8_t count = 0; count < 16; ++count)
    {
        lcd_char(' ');
    }
    
    if (p_config_local->two_line_display)
    {
        lcd_set_cursor(0,1);
        for (uint8_t count = 0; count < 16; ++count)
        {
            lcd_char(' ');
        }
    }
}
 
 
/*
 * Edits config settings for lcd (lcd_config_t members must be changed first).
 */
void lcd_reconfigure(void)
{
    uint8_t byte = 0;
    byte |= ENTRY_MODE_SET;
    byte |= (p_config_local->increment_counter << MOVE_DIRECTION_BIT);
    byte |= (p_config_local->display_shift << DISPLAY_SHIFT_BIT);
    lcd_command(byte);
 
    // Also resends cursor and blink settings
    lcd_display_on();
}
 
 
/*
 * Sets DDRAM address 0 in address counter. Also returns display from being
 * shifted to original position. DDRAM contents remain unchanged.
 */
void lcd_return_home(void)
{
    lcd_command(CURSOR_HOME);
    _delay_ms(SHORT_INSTR_DELAY_MS);
}
 
 
/*
 * Moves cursor left without changing DDRAM contents.
 */
void lcd_shift_cursor_left(uint8_t distance)
{
    uint8_t byte = 0;
    byte |= CURSOR_DISPLAY_SHIFT;
 
    for (uint8_t count = 0; count < distance; ++count)
    {
        lcd_command(byte);
    }
}
 
 
/*
 * Moves cursor right without changing DDRAM contents.
 */
void lcd_shift_cursor_right(uint8_t distance)
{
    uint8_t byte = 0;
    byte |= CURSOR_DISPLAY_SHIFT;
    byte |= (1U << RIGHT_LEFT_BIT);
 
    for (uint8_t count = 0; count < distance; ++count)
    {
        lcd_command(byte);
    }
}
 
 
/*
 * Shifts display left without changing DDRAM contents.
 */
void lcd_shift_display_left(uint8_t distance, bool delay)
{
    uint8_t byte = 0U;
    byte |= CURSOR_DISPLAY_SHIFT;
    byte |= (1U << SHIFT_OR_CURSOR_BIT);
 
    for (uint8_t count = 0; count < distance; ++count)
    {
        lcd_command(byte);
        if (delay == true)
        {
            _delay_ms(SCROLL_DELAY_MS);
        }
    }
}
 
 
/*
 * Shifts display right without changing DDRAM contents.
 */
void lcd_shift_display_right(uint8_t distance, bool delay)
{
    uint8_t byte = 0;
    byte |= CURSOR_DISPLAY_SHIFT;
    byte |= (1U << SHIFT_OR_CURSOR_BIT);
    byte |= (1U << RIGHT_LEFT_BIT);
 
    for (uint8_t count = 0; count < distance; ++count)
    {
        lcd_command(byte);
        if (delay == true)
        {
            _delay_ms(SCROLL_DELAY_MS);
        }
    }
}
 
//===========================================================================//
//---------------------------------------------------------------------------//
//                         Private utility functions                                                 //
//---------------------------------------------------------------------------//
//===========================================================================//
 
/*
 * Sends a command to the display.
 */
void lcd_command(uint8_t data)
{
    LCD_CTRL_PORT &= ~(1U << LCD_RS);
 
    if (p_config_local->eight_bit_mode)
    {
        LCD_DATA_PORT = data;
        pulse_enable();
    }
    else
    {
        uint8_t byte = 0;
 
        LCD_DATA_PORT &= ~(data_length_bitmask); // Clear relevant bits in port
        byte = (data & 0b11110000); // Keep high 4 bits only
        byte = (byte >> (7U - LCD_D7)); // Shift nibble into place
        LCD_DATA_PORT |= byte; // Send first nibble to LCD
        pulse_enable();
        
        LCD_DATA_PORT &= ~(data_length_bitmask); // Clear relevant bits in port
        byte = (data & 0b00001111); // Keep low 4 bits only
        byte = (byte << (LCD_D7 - 3U)); // Shift nibble into place
        LCD_DATA_PORT |= byte; // Send second nibble to LCD
        pulse_enable();
    }
    _delay_ms(SHORT_INSTR_DELAY_MS);
}
 
 
/*
 * Writes a single character to LCD.
 */
void lcd_char(char character)
{
    LCD_CTRL_PORT |= (1U << LCD_RS);
 
    if (p_config_local->eight_bit_mode)
    {
        LCD_DATA_PORT = character;
        pulse_enable();
    }
    else
    {
        uint8_t byte = 0;
 
        LCD_DATA_PORT &= ~(data_length_bitmask); // Clear relevant bits in port
        byte = (character & 0b11110000); // Keep high 4 bits only
        byte = (byte >> (7U - LCD_D7)); // Shift nibble into place
        LCD_DATA_PORT |= byte; // Send first nibble to LCD
        pulse_enable();
        
        LCD_DATA_PORT &= ~(data_length_bitmask); // Clear relevant bits in port
        byte = (character & 0b00001111); // Keep low 4 bits only
        byte = (byte << (LCD_D7 - 3U)); // Shift nibble into place
        LCD_DATA_PORT |= byte; // Send second nibble to LCD
        pulse_enable();
    }
    _delay_ms(SHORT_INSTR_DELAY_MS);
}
 
 
/*
 * Pulse enable pin to latch data into register.
 */
void pulse_enable(void)
{
    LCD_CTRL_PORT |= (1U << LCD_EN);
    _delay_us(ENABLE_DELAY_US);
    LCD_CTRL_PORT &= ~(1U << LCD_EN);
    _delay_us(ENABLE_DELAY_US);
}
 
/*** end of file ***/