..
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:breadcrumbs: <a href="../../index.html">Home</a> / <a href="../../index.html#software-perl">Software</a> / Perl - LCD 20x4 Bricklet

.. |device_identifier_constant| replace:: There is also a :ref:`constant <lcd_20x4_bricklet_perl_constants>` for the device identifier of this Bricklet.

.. _lcd_20x4_bricklet_perl:

Perl - LCD 20x4 Bricklet
========================

This is the description of the :ref:`Perl API bindings <api_bindings_perl>` for the :ref:`LCD 20x4 Bricklet <lcd_20x4_bricklet>`. General information and technical
specifications for the LCD 20x4 Bricklet are summarized in its :ref:`hardware description
<lcd_20x4_bricklet_description>`.

An :ref:`installation guide <api_bindings_perl_install>` for the Perl API
bindings is part of their general description.

.. _lcd_20x4_bricklet_perl_examples:


Examples
--------

The example code below is `Public Domain (CC0 1.0)
<http://creativecommons.org/publicdomain/zero/1.0/>`__.

Hello World
^^^^^^^^^^^

`Download (example_hello_world.pl) <https://github.com/Tinkerforge/lcd-20x4-bricklet/raw/master/software/examples/perl/example_hello_world.pl>`__

.. literalinclude:: LCD20x4_Bricklet_Perl_example_hello_world.pl
 :language: perl
 :linenos:
 :tab-width: 4

Button Callbacks
^^^^^^^^^^^^^^^^

`Download (example_button_callbacks.pl) <https://github.com/Tinkerforge/lcd-20x4-bricklet/raw/master/software/examples/perl/example_button_callbacks.pl>`__

.. literalinclude:: LCD20x4_Bricklet_Perl_example_button_callbacks.pl
 :language: perl
 :linenos:
 :tab-width: 4

.. _lcd_20x4_bricklet_perl_api:

API
---

Generally, every subroutine of the Perl bindings can report an error as
``Tinkerforge::Error`` object via ``croak()``. The object has a
``get_code()`` and a ``get_message()`` subroutine. There are different
error code:

* Error->ALREADY_CONNECTED = 11
* Error->NOT_CONNECTED = 12
* Error->CONNECT_FAILED = 13
* Error->INVALID_FUNCTION_ID = 21
* Error->TIMEOUT = 31
* Error->INVALID_PARAMETER = 41
* Error->FUNCTION_NOT_SUPPORTED = 42
* Error->UNKNOWN_ERROR = 43

All methods listed below are thread-safe.




Basic Functions
^^^^^^^^^^^^^^^


.. perl:function:: BrickletLCD20x4->new($uid, $ipcon)

 :param $uid: string
 :param $ipcon: IPConnection
 :rtype: BrickletLCD20x4

 Creates an object with the unique device ID ``$uid``:

 .. code-block:: perl

    $lcd_20x4 = BrickletLCD20x4->new("YOUR_DEVICE_UID", $ipcon);

 This object can then be used after the IP Connection is connected
 (see examples :ref:`above <lcd_20x4_bricklet_perl_examples>`).


.. perl:function:: BrickletLCD20x4->write_line($line, $position, $text)

 :param $line: int
 :param $position: int
 :param $text: string
 :rtype: undef

 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 <https://github.com/Tinkerforge/lcd-20x4-bricklet/raw/master/datasheets/standard_charset.pdf>`__
 for details. The Unicode example above shows how to specify non-ASCII characters
 and how to translate from Unicode to the LCD charset.
 
.. perl:function:: BrickletLCD20x4->clear_display()

 :rtype: undef

 Deletes all characters from the display.
 
.. perl:function:: BrickletLCD20x4->backlight_on()

 :rtype: undef

 Turns the backlight on.
 
.. perl:function:: BrickletLCD20x4->backlight_off()

 :rtype: undef

 Turns the backlight off.
 
.. perl:function:: BrickletLCD20x4->is_backlight_on()

 :rtype: bool

 Returns *true* if the backlight is on and *false* otherwise.
 


Advanced Functions
^^^^^^^^^^^^^^^^^^

.. perl:function:: BrickletLCD20x4->set_config($cursor, $blinking)

 :param $cursor: bool
 :param $blinking: bool
 :rtype: undef

 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 
 :perl:func:`write_line() <BrickletLCD20x4->write_line>`.
 
 The default is (*false*, *false*).
 
.. perl:function:: BrickletLCD20x4->get_config()

 :rtype: [bool, bool]

 Returns the configuration as set by :perl:func:`set_config() <BrickletLCD20x4->set_config>`.
 
 The returned array contains the elements ``cursor`` and ``blinking``.

.. perl:function:: BrickletLCD20x4->is_button_pressed($button)

 :param $button: int
 :rtype: bool

 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
 :perl:attr:`CALLBACK_BUTTON_PRESSED <BrickletLCD20x4->CALLBACK_BUTTON_PRESSED>` and :perl:attr:`CALLBACK_BUTTON_RELEASED <BrickletLCD20x4->CALLBACK_BUTTON_RELEASED>` callbacks.
 
.. perl:function:: BrickletLCD20x4->set_custom_character($index, @character)

 :param $index: int
 :param @character: [int, int, int, int, int, int, int, int]
 :rtype: undef

 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 :perl:func:`write_line() <BrickletLCD20x4->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.
 
 .. versionadded:: 2.0.1~(Plugin)
 
.. perl:function:: BrickletLCD20x4->get_custom_character($index)

 :param $index: int
 :rtype: [int, int, int, int, int, int, int, int]

 Returns the custom character for a given index, as set with
 :perl:func:`set_custom_character() <BrickletLCD20x4->set_custom_character>`.
 
 .. versionadded:: 2.0.1~(Plugin)
 
.. perl:function:: BrickletLCD20x4->set_default_text($line, $text)

 :param $line: int
 :param $text: string
 :rtype: undef

 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 :perl:func:`set_default_text_counter() <BrickletLCD20x4->set_default_text_counter>`.
 
 .. versionadded:: 2.0.2~(Plugin)
 
.. perl:function:: BrickletLCD20x4->get_default_text($line)

 :param $line: int
 :rtype: string

 Returns the default text for a given line (0-3) as set by
 :perl:func:`set_default_text() <BrickletLCD20x4->set_default_text>`.
 
 .. versionadded:: 2.0.2~(Plugin)
 
.. perl:function:: BrickletLCD20x4->set_default_text_counter($counter)

 :param $counter: int
 :rtype: undef

 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 :perl:func:`set_default_text() <BrickletLCD20x4->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 :perl:func:`set_default_text_counter() <BrickletLCD20x4->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.
 
 .. versionadded:: 2.0.2~(Plugin)
 
.. perl:function:: BrickletLCD20x4->get_default_text_counter()

 :rtype: int

 Returns the current value of the default text counter.
 
 .. versionadded:: 2.0.2~(Plugin)
 
.. perl:function:: BrickletLCD20x4->get_api_version()

 :rtype: [int, int, int]

 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.
 
.. perl:function:: BrickletLCD20x4->get_response_expected($function_id)

 :param $function_id: int
 :rtype: bool

 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
 :perl:func:`set_response_expected() <BrickletLCD20x4->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 :perl:func:`set_response_expected() <BrickletLCD20x4->set_response_expected>`
 for the list of function ID constants available for this function.
 
.. perl:function:: BrickletLCD20x4->set_response_expected($function_id, $response_expected)

 :param $function_id: int
 :param $response_expected: bool
 :rtype: undef

 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 and callbacks it is always disabled.
 
 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 constants are available for this function:
 
 * BrickletLCD20x4->FUNCTION_WRITE_LINE = 1
 * BrickletLCD20x4->FUNCTION_CLEAR_DISPLAY = 2
 * BrickletLCD20x4->FUNCTION_BACKLIGHT_ON = 3
 * BrickletLCD20x4->FUNCTION_BACKLIGHT_OFF = 4
 * BrickletLCD20x4->FUNCTION_SET_CONFIG = 6
 * BrickletLCD20x4->FUNCTION_SET_CUSTOM_CHARACTER = 11
 * BrickletLCD20x4->FUNCTION_SET_DEFAULT_TEXT = 13
 * BrickletLCD20x4->FUNCTION_SET_DEFAULT_TEXT_COUNTER = 15
 
.. perl:function:: BrickletLCD20x4->set_response_expected_all($response_expected)

 :param $response_expected: bool
 :rtype: undef

 Changes the response expected flag for all setter and callback configuration
 functions of this device at once.
 
.. perl:function:: BrickletLCD20x4->get_identity()

 :rtype: [string, string, char, [int, int, int], [int, int, int], int]

 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 :ref:`here <device_identifier>`.
 |device_identifier_constant|
 
 The returned array contains the elements ``uid``, ``connected_uid``, ``position``, ``hardware_version``, ``firmware_version`` and ``device_identifier``.



Callback Configuration Functions
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^


.. perl:function:: BrickletLCD20x4->register_callback($id, $callback)

 :param $id: int
 :param $callback: string
 :rtype: undef

 Registers a callback with ID ``$id`` to the function named ``$callback``. The
 available IDs with corresponding function signatures are listed
 :ref:`below <lcd_20x4_bricklet_perl_callbacks>`.




.. _lcd_20x4_bricklet_perl_callbacks:

Callbacks
^^^^^^^^^

Callbacks can be registered to receive
time critical or recurring data from the device. The registration is done
with the :perl:func:`register_callback() <BrickletLCD20x4->register_callback>` function of
the device object. The first parameter is the callback ID and the second
parameter the callback function name:

.. code-block:: perl

    sub my_callback
    {
        print "@_[0]";
    }

    $lcd_20x4->register_callback(BrickletLCD20x4->CALLBACK_EXAMPLE, 'my_callback')

The callback function will be called from an internal thread of the
IP Connection. In contrast to many other programming languages, variables are
not automatically shared between threads in Perl. If you want to share a global
variable between a callback function and the rest for your program it has to be
marked as ``:shared``. See the documentation of the `threads::shared
<http://perldoc.perl.org/threads/shared.html>`__ Perl module for more details.

The available constants with inherent number and type of parameters 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.

.. perl:attribute:: BrickletLCD20x4->CALLBACK_BUTTON_PRESSED

 :param $button: int


 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).
 
.. perl:attribute:: BrickletLCD20x4->CALLBACK_BUTTON_RELEASED

 :param $button: int


 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).
 


.. _lcd_20x4_bricklet_perl_constants:

Constants
^^^^^^^^^

.. perl:attribute:: BrickletLCD20x4->DEVICE_IDENTIFIER

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

 The :perl:func:`get_identity() <BrickletLCD20x4->get_identity>` function and the
 :perl:attr:`CALLBACK_ENUMERATE <IPConnection.CALLBACK_ENUMERATE>`
 callback of the IP Connection have a ``device_identifier`` parameter to specify
 the Brick's or Bricklet's type.

