A pin is the basic object to control I/O pins. It has methods to set the mode of the pin (input, output, etc) and methods to get and set the digital logic level. For analog control of a pin, see the ADC class.

Usage Model:

.. only:: port_pyboard

    All Board Pins are predefined as pyb.Pin.board.Name::

        x1_pin = pyb.Pin.board.X1

        g = pyb.Pin(pyb.Pin.board.X1, pyb.Pin.IN)

    CPU pins which correspond to the board pins are available
    as ``pyb.cpu.Name``. For the CPU pins, the names are the port letter
    followed by the pin number. On the PYBv1.0, ``pyb.Pin.board.X1`` and
    ``pyb.Pin.cpu.B6`` are the same pin.

    You can also use strings::

        g = pyb.Pin('X1', pyb.Pin.OUT_PP)

    Users can add their own names::

        MyMapperDict = { 'LeftMotorDir' : pyb.Pin.cpu.C12 }
        pyb.Pin.dict(MyMapperDict)
        g = pyb.Pin("LeftMotorDir", pyb.Pin.OUT_OD)

    and can query mappings::

        pin = pyb.Pin("LeftMotorDir")

    Users can also add their own mapping function::

        def MyMapper(pin_name):
           if pin_name == "LeftMotorDir":
               return pyb.Pin.cpu.A0

        pyb.Pin.mapper(MyMapper)

    So, if you were to call: ``pyb.Pin("LeftMotorDir", pyb.Pin.OUT_PP)``
    then ``"LeftMotorDir"`` is passed directly to the mapper function.

    To summarise, the following order determines how things get mapped into
    an ordinal pin number:

    1. Directly specify a pin object
    2. User supplied mapping function
    3. User supplied mapping (object must be usable as a dictionary key)
    4. Supply a string which matches a board pin
    5. Supply a string which matches a CPU port/pin

    You can set ``pyb.Pin.debug(True)`` to get some debug information about
    how a particular object gets mapped to a pin.

    When a pin has the ``Pin.PULL_UP`` or ``Pin.PULL_DOWN`` pull-mode enabled,
    that pin has an effective 40k Ohm resistor pulling it to 3V3 or GND
    respectively (except pin Y5 which has 11k Ohm resistors).

    Now every time a falling edge is seen on the gpio pin, the callback will be
    executed. Caution: mechanical push buttons have "bounce" and pushing or
    releasing a switch will often generate multiple edges.
    See: http://www.eng.utah.edu/~cs5780/debouncing.pdf for a detailed
    explanation, along with various techniques for debouncing.

    All pin objects go through the pin mapper to come up with one of the
    gpio pins.

.. only:: port_pyboard

    Class methods
    -------------

    .. method:: Pin.af_list()

       Returns an array of alternate functions available for this pin.

    .. method:: Pin.debug([state])

       Get or set the debugging state (``True`` or ``False`` for on or off).

    .. method:: Pin.dict([dict])

       Get or set the pin mapper dictionary.

    .. method:: Pin.mapper([fun])

       Get or set the pin mapper function.

.. only:: port_pyboard

    .. method:: pin.init(mode, pull=Pin.PULL_NONE, af=-1)

       Initialise the pin:

         - ``mode`` can be one of:

            - ``Pin.IN`` - configure the pin for input;
            - ``Pin.OUT_PP`` - configure the pin for output, with push-pull control;
            - ``Pin.OUT_OD`` - configure the pin for output, with open-drain control;
            - ``Pin.AF_PP`` - configure the pin for alternate function, pull-pull;
            - ``Pin.AF_OD`` - configure the pin for alternate function, open-drain;
            - ``Pin.ANALOG`` - configure the pin for analog.

         - ``pull`` can be one of:

            - ``Pin.PULL_NONE`` - no pull up or down resistors;
            - ``Pin.PULL_UP`` - enable the pull-up resistor;
            - ``Pin.PULL_DOWN`` - enable the pull-down resistor.

         - when mode is ``Pin.AF_PP`` or ``Pin.AF_OD``, then af can be the index or name
           of one of the alternate functions associated with a pin.

       Returns: ``None``.

.. method:: pin.value([value])

   Get or set the digital logic level of the pin:

     - With no argument, return 0 or 1 depending on the logic level of the pin.
     - With ``value`` given, set the logic level of the pin.  ``value`` can be
       anything that converts to a boolean.  If it converts to ``True``, the pin
       is set high, otherwise it is set low.

.. only:: port_pyboard

    .. method:: pin.__str__()

       Return a string describing the pin object.

    .. method:: pin.af()

       Returns the currently configured alternate-function of the pin. The
       integer returned will match one of the allowed constants for the af
       argument to the init function.

    .. method:: pin.gpio()

       Returns the base address of the GPIO block associated with this pin.

    .. method:: pin.mode()

       Returns the currently configured mode of the pin. The integer returned
       will match one of the allowed constants for the mode argument to the init
       function.

    .. method:: pin.name()

       Get the pin name.

    .. method:: pin.names()

       Returns the cpu and board names for this pin.

    .. method:: pin.pin()

       Get the pin number.

    .. method:: pin.port()

       Get the pin port.

.. method:: pin.pull()

    Returns the currently configured pull of the pin. The integer returned
    will match one of the allowed constants for the pull argument to the init
    function.

.. only:: port_pyboard

    .. data:: Pin.AF_OD

       initialise the pin to alternate-function mode with an open-drain drive

    .. data:: Pin.AF_PP

       initialise the pin to alternate-function mode with a push-pull drive

    .. data:: Pin.ANALOG

       initialise the pin to analog mode

    .. data:: Pin.IN

       initialise the pin to input mode

    .. data:: Pin.OUT_OD

       initialise the pin to output mode with an open-drain drive

    .. data:: Pin.OUT_PP

       initialise the pin to output mode with a push-pull drive

    .. data:: Pin.PULL_DOWN

       enable the pull-down resistor on the pin

    .. data:: Pin.PULL_NONE

       don't enable any pull up or down resistors on the pin

    .. data:: Pin.PULL_UP

       enable the pull-up resistor on the pin

.. only:: port_pyboard

    class PinAF -- Pin Alternate Functions
    ======================================

    A Pin represents a physical pin on the microcprocessor. Each pin
    can have a variety of functions (GPIO, I2C SDA, etc). Each PinAF
    object represents a particular function for a pin.

    Usage Model::

        x3 = pyb.Pin.board.X3
        x3_af = x3.af_list()

    x3_af will now contain an array of PinAF objects which are availble on
    pin X3.

    For the pyboard, x3_af would contain:
        [Pin.AF1_TIM2, Pin.AF2_TIM5, Pin.AF3_TIM9, Pin.AF7_USART2]

    Normally, each peripheral would configure the af automatically, but sometimes
    the same function is available on multiple pins, and having more control
    is desired.

    To configure X3 to expose TIM2_CH3, you could use::

       pin = pyb.Pin(pyb.Pin.board.X3, mode=pyb.Pin.AF_PP, af=pyb.Pin.AF1_TIM2)

    or::

       pin = pyb.Pin(pyb.Pin.board.X3, mode=pyb.Pin.AF_PP, af=1)

    Methods
    -------

    .. method:: pinaf.__str__()

       Return a string describing the alternate function.

    .. method:: pinaf.index()

       Return the alternate function index.

    .. method:: pinaf.name()

       Return the name of the alternate function.

    .. method:: pinaf.reg()

       Return the base register associated with the peripheral assigned to this
       alternate function. For example, if the alternate function were TIM2_CH3
       this would return stm.TIM2