hd44780 v0.1.0

HD44780-compatible character LCD, 4-bit parallel interface.

Application scenarios

• A two-line status display.
• A menu or parameter editor.
• A legacy panel replacement.

Contract

uint8_t hd44780_init(hd44780_t *lcd, hd44780_port_t port, uint8_t columns, uint8_t rows);
void hd44780_clear(hd44780_t *lcd);
void hd44780_set_cursor(hd44780_t *lcd, uint8_t column, uint8_t row);
void hd44780_write_char(hd44780_t *lcd, char value);
void hd44780_write_string(hd44780_t *lcd, const char *text);

• The adapter owns RS, E, and D4..D7.
• init performs the 4-bit wake-up sequence for a 5x8 font.
• set_cursor accepts 1 or 2 rows and up to 20 columns.
• Returns 1 on success, 0 for an unsupported geometry.

Parameters

• Columns 1..20; rows 1..2.
• The contrast and backlight are board concerns, not part of this unit.
• Use a 5 V-compatible level shifter when the MCU is 3.3 V.

Memory and timing

• 4 bytes; 4-bit transfers, two pulses per byte.
• Clear needs about 2 ms; other commands need about 50 us.

Integration

hd44780_t lcd;
hd44780_init(&lcd, board_hd44780_port(), 16, 2);
hd44780_set_cursor(&lcd, 0, 0);
hd44780_write_string(&lcd, "loom");

Adapters

• The adapter sets RS, writes D4..D7, and pulses E high then low.
• Reference: the HD44780 datasheet and the 4-bit sequence used by

mathertel/LiquidCrystal_PCF8574 (MIT).

• This implementation is original.

When not to use

• A graphic display; use an OLED or TFT driver.
• A long cable without buffering; the 4-bit bus is sensitive to noise.

Verification

make test covers the wake-up nibbles, a character write, cursor addressing,

and geometry rejection.

void *context;
void (*set_rs)(void *context, uint8_t level);
void (*set_enable)(void *context, uint8_t level);
void (*write_nibble)(void *context, uint8_t value);
void (*delay_ms)(void *context, uint16_t milliseconds);

hd44780_port_t port;
uint8_t columns;
uint8_t rows;