C/C++ - LCD 20x4 Bricklet

This is the description of the C/C++ API bindings for the LCD 20x4 Bricklet. General information and technical specifications for the LCD 20x4 Bricklet are summarized in its hardware description.

An installation guide for the C/C++ API bindings is part of their general description.

Examples

The example code below is Public Domain (CC0 1.0).

Hello World

Download (example_hello_world.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_lcd_20x4.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your LCD 20x4 Bricklet

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    LCD20x4 lcd;
    lcd_20x4_create(&lcd, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Turn backlight on
    lcd_20x4_backlight_on(&lcd);

    // Write "Hello World"
    lcd_20x4_write_line(&lcd, 0, 0, "Hello World");

    printf("Press key to exit\n");
    getchar();
    lcd_20x4_destroy(&lcd);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Button Callback

Download (example_button_callback.c)

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#include <stdio.h>

#include "ip_connection.h"
#include "bricklet_lcd_20x4.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your LCD 20x4 Bricklet

// Callback function for button pressed callback
void cb_button_pressed(uint8_t button, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Button Pressed: %u\n", button);
}

// Callback function for button released callback
void cb_button_released(uint8_t button, void *user_data) {
    (void)user_data; // avoid unused parameter warning

    printf("Button Released: %u\n", button);
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    LCD20x4 lcd;
    lcd_20x4_create(&lcd, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Register button pressed callback to function cb_button_pressed
    lcd_20x4_register_callback(&lcd,
                               LCD_20X4_CALLBACK_BUTTON_PRESSED,
                               (void *)cb_button_pressed,
                               NULL);

    // Register button released callback to function cb_button_released
    lcd_20x4_register_callback(&lcd,
                               LCD_20X4_CALLBACK_BUTTON_RELEASED,
                               (void *)cb_button_released,
                               NULL);

    printf("Press key to exit\n");
    getchar();
    lcd_20x4_destroy(&lcd);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

Unicode

Download (example_unicode.c)

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#include <stdio.h>
#include <wchar.h>

#include "ip_connection.h"
#include "bricklet_lcd_20x4.h"

#define HOST "localhost"
#define PORT 4223
#define UID "XYZ" // Change XYZ to the UID of your LCD 20x4 Bricklet

// Maps a wchar_t string to the LCD charset
static void wchar_to_ks0066u(const wchar_t *wchar, char *ks0066u, int ks0066u_length)
{
    const wchar_t *s = wchar;
    char *d = ks0066u;
    char *e = ks0066u + ks0066u_length;
    char c;
    uint32_t code_point;

    while (*s != '\0' && d < e) {
        // If wchar_t is UTF-16 then handle surrogates
        if (sizeof(wchar_t) == 2 && *s >= 0xd800 && *s <= 0xdbff) {
            code_point = 0x10000 + (*s - 0xd800) * 0x400 + (*(s + 1) - 0xdc00);
            s += 2;
        } else {
            code_point = *s++;
        }

        // ASCII subset from JIS X 0201
        if (code_point >= 0x0020 && code_point <= 0x007e) {
            // The LCD charset doesn't include '\' and '~', use similar characters instead
            switch (code_point) {
            case 0x005c: c = 0xa4; break; // REVERSE SOLIDUS maps to IDEOGRAPHIC COMMA
            case 0x007e: c = 0x2d; break; // TILDE maps to HYPHEN-MINUS
            default: c = code_point; break;
            }
        }
        // Katakana subset from JIS X 0201
        else if (code_point >= 0xff61 && code_point <= 0xff9f) {
            c = code_point - 0xfec0;
        }
        // Special characters
        else {
            switch (code_point) {
            case 0x00a5: c = 0x5c; break; // YEN SIGN
            case 0x2192: c = 0x7e; break; // RIGHTWARDS ARROW
            case 0x2190: c = 0x7f; break; // LEFTWARDS ARROW
            case 0x00b0: c = 0xdf; break; // DEGREE SIGN maps to KATAKANA SEMI-VOICED SOUND MARK
            case 0x03b1: c = 0xe0; break; // GREEK SMALL LETTER ALPHA
            case 0x00c4: c = 0xe1; break; // LATIN CAPITAL LETTER A WITH DIAERESIS
            case 0x00e4: c = 0xe1; break; // LATIN SMALL LETTER A WITH DIAERESIS
            case 0x00df: c = 0xe2; break; // LATIN SMALL LETTER SHARP S
            case 0x03b5: c = 0xe3; break; // GREEK SMALL LETTER EPSILON
            case 0x00b5: c = 0xe4; break; // MICRO SIGN
            case 0x03bc: c = 0xe4; break; // GREEK SMALL LETTER MU
            case 0x03c2: c = 0xe5; break; // GREEK SMALL LETTER FINAL SIGMA
            case 0x03c1: c = 0xe6; break; // GREEK SMALL LETTER RHO
            case 0x221a: c = 0xe8; break; // SQUARE ROOT
            case 0x00b9: c = 0xe9; break; // SUPERSCRIPT ONE maps to SUPERSCRIPT (minus) ONE
            case 0x00a4: c = 0xeb; break; // CURRENCY SIGN
            case 0x00a2: c = 0xec; break; // CENT SIGN
            case 0x2c60: c = 0xed; break; // LATIN CAPITAL LETTER L WITH DOUBLE BAR
            case 0x00f1: c = 0xee; break; // LATIN SMALL LETTER N WITH TILDE
            case 0x00d6: c = 0xef; break; // LATIN CAPITAL LETTER O WITH DIAERESIS
            case 0x00f6: c = 0xef; break; // LATIN SMALL LETTER O WITH DIAERESIS
            case 0x03f4: c = 0xf2; break; // GREEK CAPITAL THETA SYMBOL
            case 0x221e: c = 0xf3; break; // INFINITY
            case 0x03a9: c = 0xf4; break; // GREEK CAPITAL LETTER OMEGA
            case 0x00dc: c = 0xf5; break; // LATIN CAPITAL LETTER U WITH DIAERESIS
            case 0x00fc: c = 0xf5; break; // LATIN SMALL LETTER U WITH DIAERESIS
            case 0x03a3: c = 0xf6; break; // GREEK CAPITAL LETTER SIGMA
            case 0x03c0: c = 0xf7; break; // GREEK SMALL LETTER PI
            case 0x0304: c = 0xf8; break; // COMBINING MACRON
            case 0x00f7: c = 0xfd; break; // DIVISION SIGN

            default:
            case 0x25a0: c = 0xff; break; // BLACK SQUARE
            }
        }

        // Special handling for 'x' followed by COMBINING MACRON
        if (c == (char)0xf8) {
            if (d == ks0066u || (d > ks0066u && *(d - 1) != 'x')) {
                c = 0xff; // BLACK SQUARE
            }

            if (d > ks0066u) {
                --d;
            }
        }

        *d++ = c;
    }

    while (d < e) {
        *d++ = '\0';
    }
}

int main(void) {
    // Create IP connection
    IPConnection ipcon;
    ipcon_create(&ipcon);

    // Create device object
    LCD20x4 lcd;
    lcd_20x4_create(&lcd, UID, &ipcon);

    // Connect to brickd
    if(ipcon_connect(&ipcon, HOST, PORT) < 0) {
        fprintf(stderr, "Could not connect\n");
        return 1;
    }
    // Don't use device before ipcon is connected

    // Turn backlight on
    lcd_20x4_backlight_on(&lcd);

    // Write some strings using the wchar_to_ks0066u function to map to the LCD charset
    char ks0066u[20];

    wchar_to_ks0066u(L"Stromstärke: 17µA", ks0066u, sizeof(ks0066u));
    lcd_20x4_write_line(&lcd, 0, 0, ks0066u);

    wchar_to_ks0066u(L"Temperatur:  23°C", ks0066u, sizeof(ks0066u));
    lcd_20x4_write_line(&lcd, 1, 0, ks0066u);

    // Write a string directly including characters from the LCD charset
    lcd_20x4_write_line(&lcd, 2, 0, "Drehzahl:   750min\xe9");

    printf("Press key to exit\n");
    getchar();
    lcd_20x4_destroy(&lcd);
    ipcon_destroy(&ipcon); // Calls ipcon_disconnect internally
    return 0;
}

API

Every function of the C/C++ bindings returns an integer which describes an error code. Data returned from the device, when a getter is called, is handled via call by reference. These parameters are labeled with the ret_ prefix.

Possible error codes are:

  • E_OK = 0
  • E_TIMEOUT = -1
  • E_NO_STREAM_SOCKET = -2
  • E_HOSTNAME_INVALID = -3
  • E_NO_CONNECT = -4
  • E_NO_THREAD = -5
  • E_NOT_ADDED = -6 (unused since bindings version 2.0.0)
  • E_ALREADY_CONNECTED = -7
  • E_NOT_CONNECTED = -8
  • E_INVALID_PARAMETER = -9
  • E_NOT_SUPPORTED = -10
  • E_UNKNOWN_ERROR_CODE = -11
  • E_STREAM_OUT_OF_SYNC = -12

as defined in ip_connection.h.

All functions listed below are thread-safe.

Basic Functions

void lcd_20x4_create(LCD20x4 *lcd_20x4, const char *uid, IPConnection *ipcon)

Creates the device object lcd_20x4 with the unique device ID uid and adds it to the IPConnection ipcon:

LCD20x4 lcd_20x4;
lcd_20x4_create(&lcd_20x4, "YOUR_DEVICE_UID", &ipcon);

This device object can be used after the IP connection has been connected (see examples above).

void lcd_20x4_destroy(LCD20x4 *lcd_20x4)

Removes the device object lcd_20x4 from its IPConnection and destroys it. The device object cannot be used anymore afterwards.

int lcd_20x4_write_line(LCD20x4 *lcd_20x4, uint8_t line, uint8_t position, const char text[20])

Writes text to a specific line (0 to 3) with a specific position (0 to 19). The text can have a maximum of 20 characters.

For example: (0, 7, "Hello") will write Hello in the middle of the first line of the display.

The display uses a special charset that includes all ASCII characters except backslash and tilde. The LCD charset also includes several other non-ASCII characters, see the charset specification for details. The Unicode example above shows how to specify non-ASCII characters and how to translate from Unicode to the LCD charset.

int lcd_20x4_clear_display(LCD20x4 *lcd_20x4)

Deletes all characters from the display.

int lcd_20x4_backlight_on(LCD20x4 *lcd_20x4)

Turns the backlight on.

int lcd_20x4_backlight_off(LCD20x4 *lcd_20x4)

Turns the backlight off.

int lcd_20x4_is_backlight_on(LCD20x4 *lcd_20x4, bool *ret_backlight)

Returns true if the backlight is on and false otherwise.

Advanced Functions

int lcd_20x4_set_config(LCD20x4 *lcd_20x4, bool cursor, bool blinking)

Configures if the cursor (shown as "_") should be visible and if it should be blinking (shown as a blinking block). The cursor position is one character behind the the last text written with lcd_20x4_write_line().

The default is (false, false).

int lcd_20x4_get_config(LCD20x4 *lcd_20x4, bool *ret_cursor, bool *ret_blinking)

Returns the configuration as set by lcd_20x4_set_config().

int lcd_20x4_is_button_pressed(LCD20x4 *lcd_20x4, uint8_t button, bool *ret_pressed)

Returns true if the button (0 to 2 or 0 to 3 since hardware version 1.2) is pressed.

If you want to react on button presses and releases it is recommended to use the LCD_20X4_CALLBACK_BUTTON_PRESSED and LCD_20X4_CALLBACK_BUTTON_RELEASED callbacks.

int lcd_20x4_set_custom_character(LCD20x4 *lcd_20x4, uint8_t index, uint8_t character[8])

The LCD 20x4 Bricklet can store up to 8 custom characters. The characters consist of 5x8 pixels and can be addressed with the index 0-7. To describe the pixels, the first 5 bits of 8 bytes are used. For example, to make a custom character "H", you should transfer the following:

  • character[0] = 0b00010001 (decimal value 17)
  • character[1] = 0b00010001 (decimal value 17)
  • character[2] = 0b00010001 (decimal value 17)
  • character[3] = 0b00011111 (decimal value 31)
  • character[4] = 0b00010001 (decimal value 17)
  • character[5] = 0b00010001 (decimal value 17)
  • character[6] = 0b00010001 (decimal value 17)
  • character[7] = 0b00000000 (decimal value 0)

The characters can later be written with lcd_20x4_write_line() by using the characters with the byte representation 8 ("x08") to 15 ("x0F").

You can play around with the custom characters in Brick Viewer version since 2.0.1.

Custom characters are stored by the LCD in RAM, so they have to be set after each startup.

New in version 2.0.1 (Plugin).

int lcd_20x4_get_custom_character(LCD20x4 *lcd_20x4, uint8_t index, uint8_t ret_character[8])

Returns the custom character for a given index, as set with lcd_20x4_set_custom_character().

New in version 2.0.1 (Plugin).

int lcd_20x4_set_default_text(LCD20x4 *lcd_20x4, uint8_t line, const char text[20])

Sets the default text for lines 0-3. The max number of characters per line is 20.

The default text is shown on the LCD, if the default text counter expires, see lcd_20x4_set_default_text_counter().

New in version 2.0.2 (Plugin).

int lcd_20x4_get_default_text(LCD20x4 *lcd_20x4, uint8_t line, char ret_text[20])

Returns the default text for a given line (0-3) as set by lcd_20x4_set_default_text().

New in version 2.0.2 (Plugin).

int lcd_20x4_set_default_text_counter(LCD20x4 *lcd_20x4, int32_t counter)

Sets the default text counter in ms. This counter is decremented each ms by the LCD firmware. If the counter reaches 0, the default text (see lcd_20x4_set_default_text()) is shown on the LCD.

This functionality can be used to show a default text if the controlling program crashes or the connection is interrupted.

A possible approach is to call lcd_20x4_set_default_text_counter() every minute with the parameter 1000*60*2 (2 minutes). In this case the default text will be shown no later than 2 minutes after the controlling program crashes.

A negative counter turns the default text functionality off.

The default is -1.

New in version 2.0.2 (Plugin).

int lcd_20x4_get_default_text_counter(LCD20x4 *lcd_20x4, int32_t *ret_counter)

Returns the current value of the default text counter.

New in version 2.0.2 (Plugin).

int lcd_20x4_get_api_version(LCD20x4 *lcd_20x4, uint8_t ret_api_version[3])

Returns the version of the API definition (major, minor, revision) implemented by this API bindings. This is neither the release version of this API bindings nor does it tell you anything about the represented Brick or Bricklet.

int lcd_20x4_get_response_expected(LCD20x4 *lcd_20x4, uint8_t function_id, bool *ret_response_expected)

Returns the response expected flag for the function specified by the function ID parameter. It is true if the function is expected to send a response, false otherwise.

For getter functions this is enabled by default and cannot be disabled, because those functions will always send a response. For callback configuration functions it is enabled by default too, but can be disabled by lcd_20x4_set_response_expected(). For setter functions it is disabled by default and can be enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

See lcd_20x4_set_response_expected() for the list of function ID defines available for this function.

int lcd_20x4_set_response_expected(LCD20x4 *lcd_20x4, uint8_t function_id, bool response_expected)

Changes the response expected flag of the function specified by the function ID parameter. This flag can only be changed for setter (default value: false) and callback configuration functions (default value: true). For getter functions it is always enabled.

Enabling the response expected flag for a setter function allows to detect timeouts and other error conditions calls of this setter as well. The device will then send a response for this purpose. If this flag is disabled for a setter function then no response is send and errors are silently ignored, because they cannot be detected.

The following function ID defines are available for this function:

  • LCD_20X4_FUNCTION_WRITE_LINE = 1
  • LCD_20X4_FUNCTION_CLEAR_DISPLAY = 2
  • LCD_20X4_FUNCTION_BACKLIGHT_ON = 3
  • LCD_20X4_FUNCTION_BACKLIGHT_OFF = 4
  • LCD_20X4_FUNCTION_SET_CONFIG = 6
  • LCD_20X4_FUNCTION_SET_CUSTOM_CHARACTER = 11
  • LCD_20X4_FUNCTION_SET_DEFAULT_TEXT = 13
  • LCD_20X4_FUNCTION_SET_DEFAULT_TEXT_COUNTER = 15
int lcd_20x4_set_response_expected_all(LCD20x4 *lcd_20x4, bool response_expected)

Changes the response expected flag for all setter and callback configuration functions of this device at once.

int lcd_20x4_get_identity(LCD20x4 *lcd_20x4, char ret_uid[8], char ret_connected_uid[8], char *ret_position, uint8_t ret_hardware_version[3], uint8_t ret_firmware_version[3], uint16_t *ret_device_identifier)

Returns the UID, the UID where the Bricklet is connected to, the position, the hardware and firmware version as well as the device identifier.

The position can be 'a', 'b', 'c' or 'd'.

The device identifier numbers can be found here. There is also a constant for the device identifier of this Bricklet.

Callback Configuration Functions

void lcd_20x4_register_callback(LCD20x4 *lcd_20x4, int16_t callback_id, void *function, void *user_data)

Registers the given function with the given callback_id. The user_data will be passed as the last parameter to the function.

The available callback IDs with corresponding function signatures are listed below.

Callbacks

Callbacks can be registered to receive time critical or recurring data from the device. The registration is done with the lcd_20x4_register_callback() function. The parameters consist of the device object, the callback ID, the callback function and optional user data:

void my_callback(int p, void *user_data) {
    printf("parameter: %d\n", p);
}

lcd_20x4_register_callback(&lcd_20x4, LCD_20X4_CALLBACK_EXAMPLE, (void *)my_callback, NULL);

The available constants with corresponding callback function signatures are described below.

Note

Using callbacks for recurring events is always preferred compared to using getters. It will use less USB bandwidth and the latency will be a lot better, since there is no round trip time.

LCD_20X4_CALLBACK_BUTTON_PRESSED
void callback(uint8_t button, void *user_data)

This callback is triggered when a button is pressed. The parameter is the number of the button (0 to 2 or 0 to 3 since hardware version 1.2).

LCD_20X4_CALLBACK_BUTTON_RELEASED
void callback(uint8_t button, void *user_data)

This callback is triggered when a button is released. The parameter is the number of the button (0 to 2 or 0 to 3 since hardware version 1.2).

Constants

LCD_20X4_DEVICE_IDENTIFIER

This constant is used to identify a LCD 20x4 Bricklet.

The lcd_20x4_get_identity() function and the IPCON_CALLBACK_ENUMERATE callback of the IP Connection have a device_identifier parameter to specify the Brick's or Bricklet's type.

LCD_20X4_DEVICE_DISPLAY_NAME

This constant represents the human readable name of a LCD 20x4 Bricklet.