qmk-firmware/docs/features/hd44780.md

HD44780 LCD Driver

Supported Hardware

LCD modules using HD44780U IC or equivalent, communicating in 4-bit mode.

Module	Size	Notes
1602A	16x2, 5x8 dots
2004A	20x4, 5x8 dots	Untested, not currently supported

To run these modules at 3.3V, an additional MAX660 voltage converter IC must be soldered on, along with two 10µF capacitors. See this page for more details.

Usage

Add the following to your rules.mk:

HD44780_ENABLE = yes

Basic Configuration

Add the following to your config.h:

Define	Default	Description
HD44780_DATA_PINS	Not defined	(Required) An array of four GPIO pins connected to the display's D4-D7 pins, eg. { B1, B3, B2, B6 }
HD44780_RS_PIN	Not defined	(Required) The GPIO connected to the display's RS pin
HD44780_RW_PIN	Not defined	(Required) The GPIO connected to the display's RW pin
HD44780_E_PIN	Not defined	(Required) The GPIO connected to the display's E pin
HD44780_DISPLAY_COLS	16	The number of visible characters on a single line of the display
HD44780_DISPLAY_LINES	2	The number of visible lines on the display
HD44780_WRAP_LINES	Not defined	If defined, input characters will wrap to the next line

Examples

Hello World

Add the following to your keymap.c:

void keyboard_post_init_user(void) {
    hd44780_init(true, true); // Show blinking cursor
    hd44780_puts_P(PSTR("Hello, world!\n"));
}

Custom Character Definition

Up to eight custom characters can be defined. This data is stored in the Character Generator RAM (CGRAM), and is not persistent across power cycles.

This example defines the QMK Psi as the first custom character. The first 16 positions in the character set are reserved for the eight custom characters duplicated.

Byte |      16 8 4 2 1
   1 | x x x ■ □ ■ □ ■
   2 | x x x ■ □ ■ □ ■
   3 | x x x ■ □ ■ □ ■
   4 | x x x □ ■ ■ ■ □
   5 | x x x □ □ ■ □ □
   6 | x x x □ □ ■ □ □
   7 | x x x □ □ ■ □ □
   8 | x x x □ □ □ □ □

const uint8_t PROGMEM psi[8] = { 0x15, 0x15, 0x15, 0x0E, 0x04, 0x04, 0x04, 0x00 };

void keyboard_post_init_user(void) {
    hd44780_init(false, false);
    hd44780_define_char_P(0, psi);
    // Cursor is incremented while defining characters so must be reset
    hd44780_home();
    // 0x08 to avoid null terminator
    hd44780_puts_P(PSTR("\x08 QMK Firmware"));
}

API

void hd44780_init(bool cursor, bool blink)

Initialize the display.

This function should be called only once, before any of the other functions can be called.

Arguments

• bool cursor
  Whether to show the cursor.
• bool blink
  Whether to blink the cursor, if shown.

---

void hd44780_clear(void)

Clear the display.

This function is called on init.

---

void hd44780_home(void)

Move the cursor to the home position.

This function is called on init.

---

void hd44780_on(bool cursor, bool blink)

Turn the display on, and/or set the cursor properties.

This function is called on init.

Arguments

• bool cursor
  Whether to show the cursor.
• bool blink
  Whether to blink the cursor, if shown.

---

void hd44780_off(void)

Turn the display off.

---

void hd44780_set_cursor(uint8_t col, uint8_t line)

Move the cursor to the specified position on the display.

Arguments

• uint8_t col
  The column number to move to, from 0 to 15 on 16x2 displays.
• bool line
  The line number to move to, either 0 or 1 on 16x2 displays.

---

void hd44780_putc(char c)

Print a character to the display. The newline character \n will move the cursor to the start of the next line.

The exact character shown may depend on the ROM code of your particular display - refer to the datasheet for the full character set.

Arguments

• char c
  The character to print.

---

void hd44780_puts(const char *s)

Print a string of characters to the display.

Arguments

• const char *s
  The string to print.

---

void hd44780_puts_P(const char *s)

Print a string of characters from PROGMEM to the display.

On ARM devices, this function is simply an alias of hd44780_puts().

Arguments

• const char *s
  The PROGMEM string to print (ie. PSTR("Hello")).

---

void hd44780_define_char(uint8_t index, uint8_t *data)

Define a custom character.

Arguments

• uint8_t index
  The index of the custom character to define, from 0 to 7.
• uint8_t *data
  An array of 8 bytes containing the 5-bit row data of the character, where the first byte is the topmost row, and the least significant bit of each byte is the rightmost column.

---

void hd44780_define_char_P(uint8_t index, const uint8_t *data)

Define a custom character from PROGMEM.

On ARM devices, this function is simply an alias of hd44780_define_char().

Arguments

• uint8_t index
  The index of the custom character to define, from 0 to 7.
• const uint8_t *data
  A PROGMEM array of 8 bytes containing the 5-bit row data of the character, where the first byte is the topmost row, and the least significant bit of each byte is the rightmost column.

---

bool hd44780_busy(void)

Indicates whether the display is currently processing, and cannot accept instructions.

Return Value

true if the display is busy.

---

void hd44780_write(uint8_t data, bool isData)

Write a byte to the display.

Arguments

• uint8_t data
  The byte to send to the display.
• bool isData
  Whether the byte is an instruction or character data.

---

uint8_t hd44780_read(bool isData)

Read a byte from the display.

Arguments

• bool isData
  Whether to read the current cursor position, or the character at the cursor.

Return Value

If isData is true, the returned byte will be the character at the current DDRAM address. Otherwise, it will be the current DDRAM address and the busy flag.

---

void hd44780_command(uint8_t command)

Send a command to the display. Refer to the datasheet and hd44780.h for the valid commands and defines.

This function waits for the display to clear the busy flag before sending the command.

Arguments

• uint8_t command
  The command to send.

---

void hd44780_data(uint8_t data)

Send a byte of data to the display.

This function waits for the display to clear the busy flag before sending the data.

Arguments

• uint8_t data
  The byte of data to send.

---

void hd44780_set_cgram_address(uint8_t address)

Set the CGRAM address.

This function is used when defining custom characters.

Arguments

• uint8_t address
  The CGRAM address to move to, from 0x00 to 0x3F.

---

void hd44780_set_ddram_address(uint8_t address)

Set the DDRAM address.

This function is used when printing characters to the display, and setting the cursor.

Arguments

• uint8_t address
  The DDRAM address to move to, from 0x00 to 0x7F.