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circuitpython/docs/library/machine.Pin.rst

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.. currentmodule:: machine
class Pin -- control I/O pins
=============================
A pin object is used to control I/O pins (also known as GPIO - general-purpose
input/output). Pin objects are commonly associated with a physical pin that can
drive an output voltage and read input voltages. The pin class has methods to set the mode of
the pin (IN, OUT, etc) and methods to get and set the digital logic level.
For analog control of a pin, see the :class:`ADC` class.
A pin object is constructed by using an identifier which unambiguously
specifies a certain I/O pin. The allowed forms of the identifier and the
physical pin that the identifier maps to are port-specific. Possibilities
for the identifier are an integer, a string or a tuple with port and pin
number.
Usage Model::
from machine import Pin
# create an output pin on pin #0
p0 = Pin(0, Pin.OUT)
# set the value low then high
p0.value(0)
p0.value(1)
# create an input pin on pin #2, with a pull up resistor
p2 = Pin(2, Pin.IN, Pin.PULL_UP)
# read and print the pin value
print(p2.value())
# reconfigure pin #0 in input mode
p0.mode(p0.IN)
# configure an irq callback
p0.irq(lambda p:print(p))
.. only:: port_wipy
On the WiPy board the pins are identified by their string id::
from machine import Pin
g = machine.Pin('GP9', mode=Pin.OUT, pull=None, drive=Pin.MED_POWER, alt=-1)
You can also configure the Pin to generate interrupts. For instance::
from machine import Pin
def pincb(pin):
print(pin.id())
pin_int = Pin('GP10', mode=Pin.IN, pull=Pin.PULL_DOWN)
pin_int.irq(trigger=Pin.IRQ_RISING, handler=pincb)
# the callback can be triggered manually
pin_int.irq()()
# to disable the callback
pin_int.irq().disable()
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.
For the ``drive`` parameter the strengths are:
- ``Pin.LOW_POWER`` - 2mA drive capability.
- ``Pin.MED_POWER`` - 4mA drive capability.
- ``Pin.HIGH_POWER`` - 6mA drive capability.
For the ``alt`` parameter please refer to the pinout and alternate functions
table at <https://raw.githubusercontent.com/wipy/wipy/master/docs/PinOUT.png>`_
for the specific alternate functions that each pin supports.
For interrupts, the ``priority`` can take values in the range 1-7. And the
``wake`` parameter has the following properties:
- If ``wake_from=machine.Sleep.ACTIVE`` any pin can wake the board.
- If ``wake_from=machine.Sleep.SUSPENDED`` pins ``GP2``, ``GP4``, ``GP10``,
``GP11``, GP17`` or ``GP24`` can wake the board. Note that only 1
of this pins can be enabled as a wake source at the same time, so, only
the last enabled pin as a ``machine.Sleep.SUSPENDED`` wake source will have effect.
- If ``wake_from=machine.Sleep.SUSPENDED`` pins ``GP2``, ``GP4``, ``GP10``,
``GP11``, ``GP17`` and ``GP24`` can wake the board. In this case all of the
6 pins can be enabled as a ``machine.Sleep.HIBERNATE`` wake source at the same time.
Constructors
------------
.. class:: Pin(id, mode=-1, pull=-1, \*, value, drive, alt)
Access the pin peripheral (GPIO pin) associated with the given ``id``. If
additional arguments are given in the constructor then they are used to initialise
the pin. Any settings that are not specified will remain in their previous state.
The arguments are:
- ``id`` is mandatory and can be an arbitrary object. Among possible value
types are: int (an internal Pin identifier), str (a Pin name), and tuple
(pair of [port, pin]).
- ``mode`` specifies the pin mode, which can be one of:
- ``Pin.IN`` - Pin is configured for input. If viewed as an output the pin
is in high-impedance state.
- ``Pin.OUT`` - Pin is configured for (normal) output.
- ``Pin.OPEN_DRAIN`` - Pin is configured for open-drain output. Open-drain
output works in the following way: if the output value is set to 0 the pin
is active at a low level; if the output value is 1 the pin is in a high-impedance
state. Not all ports implement this mode, or some might only on certain pins.
- ``Pin.ALT`` - Pin is configured to perform an alternative function, which is
port specific. For a pin configured in such a way any other Pin methods
(except :meth:`Pin.init`) are not applicable (calling them will lead to undefined,
or a hardware-specific, result). Not all ports implement this mode.
- ``Pin.ALT_OPEN_DRAIN`` - The Same as ``Pin.ALT``, but the pin is configured as
open-drain. Not all ports implement this mode.
- ``pull`` specifies if the pin has a (weak) pull resistor attached, and can be
one of:
- ``None`` - No pull up or down resistor.
- ``Pin.PULL_UP`` - Pull up resistor enabled.
- ``Pin.PULL_DOWN`` - Pull down resistor enabled.
- ``value`` is valid only for Pin.OUT and Pin.OPEN_DRAIN modes and specifies initial
output pin value if given, otherwise the state of the pin peripheral remains
unchanged.
- ``drive`` specifies the output power of the pin and can be one of: ``Pin.LOW_POWER``,
``Pin.MED_POWER`` or ``Pin.HIGH_POWER``. The actual current driving capabilities
are port dependent. Not all ports implement this argument.
- ``alt`` specifies an alternate function for the pin and the values it can take are
port dependent. This argument is valid only for ``Pin.ALT`` and ``Pin.ALT_OPEN_DRAIN``
modes. It may be used when a pin supports more than one alternate function. If only
one pin alternate function is supported the this argument is not required. Not all
ports implement this argument.
As specified above, the Pin class allows to set an alternate function for a particular
pin, but it does not specify any further operations on such a pin. Pins configured in
alternate-function mode are usually not used as GPIO but are instead driven by other
hardware peripherals. The only operation supported on such a pin is re-initialising,
by calling the constructor or :meth:`Pin.init` method. If a pin that is configured in
alternate-function mode is re-initialised with ``Pin.IN``, ``Pin.OUT``, or
``Pin.OPEN_DRAIN``, the alternate function will be removed from the pin.
Methods
-------
.. method:: Pin.init(mode=-1, pull=-1, \*, value, drive, alt)
Re-initialise the pin using the given parameters. Only those arguments that
are specified will be set. The rest of the pin peripheral state will remain
unchanged. See the constructor documentation for details of the arguments.
Returns ``None``.
.. method:: Pin.value([x])
This method allows to set and get the value of the pin, depending on whether
the argument ``x`` is supplied or not.
If the argument is omitted then this method gets the digital logic level of
the pin, returning 0 or 1 corresponding to low and high voltage signals
respectively. The behaviour of this method depends on the mode of the pin:
- ``Pin.IN`` - The method returns the actual input value currently present
on the pin.
- ``Pin.OUT`` - The behaviour and return value of the method is undefined.
- ``Pin.OPEN_DRAIN`` - If the pin is in state '0' then the behaviour and
return value of the method is undefined. Otherwise, if the pin is in
state '1', the method returns the actual input value currently present
on the pin.
If the argument is supplied then this method sets the digital logic level of
the pin. The argument ``x`` can be anything that converts to a boolean.
If it converts to ``True``, the pin is set to state '1', otherwise it is set
to state '0'. The behaviour of this method depends on the mode of the pin:
- ``Pin.IN`` - The value is stored in the output buffer for the pin. The
pin state does not change, it remains in the high-impedance state. The
stored value will become active on the pin as soon as it is changed to
``Pin.OUT`` or ``Pin.OPEN_DRAIN`` mode.
- ``Pin.OUT`` - The output buffer is set to the given value immediately.
- ``Pin.OPEN_DRAIN`` - If the value is '0' the pin is set to a low voltage
state. Otherwise the pin is set to high-impedance state.
When setting the value this method returns ``None``.
.. method:: Pin.out_value()
Return the value stored in the output buffer of a pin, regardless of its mode.
Not all ports implement this method.
.. method:: Pin.__call__([x])
Pin objects are callable. The call method provides a (fast) shortcut to set
and get the value of the pin. It is equivalent to Pin.value([x]).
See :meth:`Pin.value` for more details.
.. method:: Pin.toggle()
Toggle the output value of the pin. Equivalent to ``pin.value(not pin.out_value())``.
Returns ``None``.
Not all ports implement this method.
Availability: WiPy.
.. method:: Pin.id()
Get the pin identifier. This may return the ``id`` as specified in the
constructor. Or it may return a canonical software-specific pin id.
.. method:: Pin.mode([mode])
Get or set the pin mode.
See the constructor documentation for details of the ``mode`` argument.
.. method:: Pin.pull([pull])
Get or set the pin pull state.
See the constructor documentation for details of the ``pull`` argument.
.. method:: Pin.drive([drive])
Get or set the pin drive strength.
See the constructor documentation for details of the ``drive`` argument.
Not all ports implement this method.
Availability: WiPy.
.. method:: Pin.irq(handler=None, trigger=(Pin.IRQ_FALLING | Pin.IRQ_RISING), \*, priority=1, wake=None)
Configure an interrupt handler to be called when the trigger source of the
pin is active. If the pin mode is ``Pin.IN`` then the trigger source is
the external value on the pin. If the pin mode is ``Pin.OUT`` then the
trigger source is the output buffer of the pin. Otherwise, if the pin mode
is ``Pin.OPEN_DRAIN`` then the trigger source is the output buffer for
state '0' and the external pin value for state '1'.
The arguments are:
- ``handler`` is an optional function to be called when the interrupt
triggers.
- ``trigger`` configures the event which can generate an interrupt.
Possible values are:
- ``Pin.IRQ_FALLING`` interrupt on falling edge.
- ``Pin.IRQ_RISING`` interrupt on rising edge.
- ``Pin.IRQ_LOW_LEVEL`` interrupt on low level.
- ``Pin.IRQ_HIGH_LEVEL`` interrupt on high level.
These values can be OR'ed together to trigger on multiple events.
- ``priority`` sets the priority level of the interrupt. The values it
can take are port-specific, but higher values always represent higher
priorities.
- ``wake`` selects the power mode in which this interrupt can wake up the
system. It can be ``machine.IDLE``, ``machine.SLEEP`` or ``machine.DEEPSLEEP``.
These values can also be OR'ed together to make a pin generate interrupts in
more than one power mode.
This method returns a callback object.
.. only:: port_wipy
.. method:: Pin.alt_list()
Returns a list of the alternate functions supported by the pin. List items are
a tuple of the form: ``('ALT_FUN_NAME', ALT_FUN_INDEX)``
Availability: WiPy.
Attributes
----------
.. class:: Pin.board
Contains all ``Pin`` objects supported by the board. Examples::
Pin.board.GP25
led = Pin(Pin.board.GP25, mode=Pin.OUT)
Pin.board.GP2.alt_list()
Availability: WiPy.
Constants
---------
The following constants are used to configure the pin objects. Note that
not all constants are available on all ports.
.. data:: Pin.IN
Pin.OUT
Pin.OPEN_DRAIN
Pin.ALT
Pin.ALT_OPEN_DRAIN
Selects the pin mode.
.. data:: Pin.PULL_UP
Pin.PULL_DOWN
Selects whether there is a pull up/down resistor. Use the value
``None`` for no pull.
.. data:: Pin.LOW_POWER
Pin.MED_POWER
Pin.HIGH_POWER
Selects the pin drive strength.
.. data:: Pin.IRQ_FALLING
Pin.IRQ_RISING
Pin.IRQ_LOW_LEVEL
Pin.IRQ_HIGH_LEVEL
Selects the IRQ trigger type.
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