circuitpython/docs/library/pyb.Pin.rst

.. currentmodule:: pyb
.. _pyb.Pin:

class Pin -- control I/O pins
=============================

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:

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.Pin.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.A0`` 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.

Constructors
------------

.. class:: pyb.Pin(id, ...)

   Create a new Pin object associated with the id.  If additional arguments are given,
   they are used to initialise the pin.  See :meth:`pin.init`.

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

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

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

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

   Get or set the pin mapper dictionary.

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

   Get or set the pin mapper function.


Methods
-------

.. method:: Pin.init(mode, pull=Pin.PULL_NONE, *, value=None, alt=-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.

     - *value* if not None will set the port output value before enabling the pin.

     - *alt* can be used when mode is ``Pin.AF_PP`` or ``Pin.AF_OD`` to set the
       index or name of one of the alternate functions associated with a pin.
       This arg was previously called *af* which can still be used if needed.

   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.

.. 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.af_list()

   Returns an array of alternate functions available for this pin.

.. 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.

Constants
---------

.. 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

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

A Pin represents a physical pin on the microprocessor. 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 available 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 alternate function 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, alt=pyb.Pin.AF1_TIM2)

or::

   pin = pyb.Pin(pyb.Pin.board.X3, mode=pyb.Pin.AF_PP, alt=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