277 lines
10 KiB
ReStructuredText
277 lines
10 KiB
ReStructuredText
.. currentmodule:: machine
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.. _machine.Pin:
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class Pin -- control I/O pins
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=============================
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A pin object is used to control I/O pins (also known as GPIO - general-purpose
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input/output). Pin objects are commonly associated with a physical pin that can
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drive an output voltage and read input voltages. The pin class has methods to set the mode of
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the pin (IN, OUT, etc) and methods to get and set the digital logic level.
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For analog control of a pin, see the :class:`ADC` class.
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A pin object is constructed by using an identifier which unambiguously
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specifies a certain I/O pin. The allowed forms of the identifier and the
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physical pin that the identifier maps to are port-specific. Possibilities
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for the identifier are an integer, a string or a tuple with port and pin
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number.
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Usage Model::
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from machine import Pin
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# create an output pin on pin #0
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p0 = Pin(0, Pin.OUT)
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# set the value low then high
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p0.value(0)
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p0.value(1)
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# create an input pin on pin #2, with a pull up resistor
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p2 = Pin(2, Pin.IN, Pin.PULL_UP)
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# read and print the pin value
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print(p2.value())
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# reconfigure pin #0 in input mode with a pull down resistor
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p0.init(p0.IN, p0.PULL_DOWN)
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# configure an irq callback
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p0.irq(lambda p:print(p))
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Constructors
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------------
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.. class:: Pin(id, mode=-1, pull=-1, *, value=None, drive=0, alt=-1)
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Access the pin peripheral (GPIO pin) associated with the given ``id``. If
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additional arguments are given in the constructor then they are used to initialise
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the pin. Any settings that are not specified will remain in their previous state.
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The arguments are:
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- ``id`` is mandatory and can be an arbitrary object. Among possible value
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types are: int (an internal Pin identifier), str (a Pin name), and tuple
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(pair of [port, pin]).
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- ``mode`` specifies the pin mode, which can be one of:
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- ``Pin.IN`` - Pin is configured for input. If viewed as an output the pin
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is in high-impedance state.
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- ``Pin.OUT`` - Pin is configured for (normal) output.
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- ``Pin.OPEN_DRAIN`` - Pin is configured for open-drain output. Open-drain
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output works in the following way: if the output value is set to 0 the pin
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is active at a low level; if the output value is 1 the pin is in a high-impedance
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state. Not all ports implement this mode, or some might only on certain pins.
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- ``Pin.ALT`` - Pin is configured to perform an alternative function, which is
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port specific. For a pin configured in such a way any other Pin methods
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(except :meth:`Pin.init`) are not applicable (calling them will lead to undefined,
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or a hardware-specific, result). Not all ports implement this mode.
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- ``Pin.ALT_OPEN_DRAIN`` - The Same as ``Pin.ALT``, but the pin is configured as
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open-drain. Not all ports implement this mode.
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- ``Pin.ANALOG`` - Pin is configured for analog input, see the :class:`ADC` class.
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- ``pull`` specifies if the pin has a (weak) pull resistor attached, and can be
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one of:
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- ``None`` - No pull up or down resistor.
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- ``Pin.PULL_UP`` - Pull up resistor enabled.
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- ``Pin.PULL_DOWN`` - Pull down resistor enabled.
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- ``value`` is valid only for Pin.OUT and Pin.OPEN_DRAIN modes and specifies initial
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output pin value if given, otherwise the state of the pin peripheral remains
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unchanged.
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- ``drive`` specifies the output power of the pin and can be one of: ``Pin.DRIVE_0``,
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``Pin.DRIVE_1``, etc., increasing in drive strength. The actual current driving
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capabilities are port dependent. Not all ports implement this argument.
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- ``alt`` specifies an alternate function for the pin and the values it can take are
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port dependent. This argument is valid only for ``Pin.ALT`` and ``Pin.ALT_OPEN_DRAIN``
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modes. It may be used when a pin supports more than one alternate function. If only
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one pin alternate function is supported the this argument is not required. Not all
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ports implement this argument.
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As specified above, the Pin class allows to set an alternate function for a particular
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pin, but it does not specify any further operations on such a pin. Pins configured in
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alternate-function mode are usually not used as GPIO but are instead driven by other
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hardware peripherals. The only operation supported on such a pin is re-initialising,
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by calling the constructor or :meth:`Pin.init` method. If a pin that is configured in
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alternate-function mode is re-initialised with ``Pin.IN``, ``Pin.OUT``, or
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``Pin.OPEN_DRAIN``, the alternate function will be removed from the pin.
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Methods
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-------
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.. method:: Pin.init(mode=-1, pull=-1, *, value=None, drive=0, alt=-1)
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Re-initialise the pin using the given parameters. Only those arguments that
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are specified will be set. The rest of the pin peripheral state will remain
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unchanged. See the constructor documentation for details of the arguments.
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Returns ``None``.
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.. method:: Pin.value([x])
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This method allows to set and get the value of the pin, depending on whether
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the argument ``x`` is supplied or not.
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If the argument is omitted then this method gets the digital logic level of
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the pin, returning 0 or 1 corresponding to low and high voltage signals
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respectively. The behaviour of this method depends on the mode of the pin:
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- ``Pin.IN`` - The method returns the actual input value currently present
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on the pin.
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- ``Pin.OUT`` - The behaviour and return value of the method is undefined.
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- ``Pin.OPEN_DRAIN`` - If the pin is in state '0' then the behaviour and
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return value of the method is undefined. Otherwise, if the pin is in
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state '1', the method returns the actual input value currently present
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on the pin.
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If the argument is supplied then this method sets the digital logic level of
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the pin. The argument ``x`` can be anything that converts to a boolean.
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If it converts to ``True``, the pin is set to state '1', otherwise it is set
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to state '0'. The behaviour of this method depends on the mode of the pin:
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- ``Pin.IN`` - The value is stored in the output buffer for the pin. The
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pin state does not change, it remains in the high-impedance state. The
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stored value will become active on the pin as soon as it is changed to
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``Pin.OUT`` or ``Pin.OPEN_DRAIN`` mode.
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- ``Pin.OUT`` - The output buffer is set to the given value immediately.
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- ``Pin.OPEN_DRAIN`` - If the value is '0' the pin is set to a low voltage
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state. Otherwise the pin is set to high-impedance state.
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When setting the value this method returns ``None``.
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.. method:: Pin.__call__([x])
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Pin objects are callable. The call method provides a (fast) shortcut to set
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and get the value of the pin. It is equivalent to Pin.value([x]).
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See :meth:`Pin.value` for more details.
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.. method:: Pin.on()
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Set pin to "1" output level.
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.. method:: Pin.off()
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Set pin to "0" output level.
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.. method:: Pin.irq(handler=None, trigger=(Pin.IRQ_FALLING | Pin.IRQ_RISING), *, priority=1, wake=None, hard=False)
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Configure an interrupt handler to be called when the trigger source of the
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pin is active. If the pin mode is ``Pin.IN`` then the trigger source is
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the external value on the pin. If the pin mode is ``Pin.OUT`` then the
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trigger source is the output buffer of the pin. Otherwise, if the pin mode
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is ``Pin.OPEN_DRAIN`` then the trigger source is the output buffer for
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state '0' and the external pin value for state '1'.
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The arguments are:
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- ``handler`` is an optional function to be called when the interrupt
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triggers. The handler must take exactly one argument which is the
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``Pin`` instance.
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- ``trigger`` configures the event which can generate an interrupt.
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Possible values are:
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- ``Pin.IRQ_FALLING`` interrupt on falling edge.
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- ``Pin.IRQ_RISING`` interrupt on rising edge.
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- ``Pin.IRQ_LOW_LEVEL`` interrupt on low level.
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- ``Pin.IRQ_HIGH_LEVEL`` interrupt on high level.
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These values can be OR'ed together to trigger on multiple events.
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- ``priority`` sets the priority level of the interrupt. The values it
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can take are port-specific, but higher values always represent higher
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priorities.
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- ``wake`` selects the power mode in which this interrupt can wake up the
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system. It can be ``machine.IDLE``, ``machine.SLEEP`` or ``machine.DEEPSLEEP``.
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These values can also be OR'ed together to make a pin generate interrupts in
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more than one power mode.
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- ``hard`` if true a hardware interrupt is used. This reduces the delay
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between the pin change and the handler being called. Hard interrupt
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handlers may not allocate memory; see :ref:`isr_rules`.
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Not all ports support this argument.
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This method returns a callback object.
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The following methods are not part of the core Pin API and only implemented on certain ports.
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.. method:: Pin.low()
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Set pin to "0" output level.
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Availability: nrf, rp2, stm32 ports.
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.. method:: Pin.high()
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Set pin to "1" output level.
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Availability: nrf, rp2, stm32 ports.
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.. method:: Pin.mode([mode])
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Get or set the pin mode.
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See the constructor documentation for details of the ``mode`` argument.
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Availability: cc3200, stm32 ports.
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.. method:: Pin.pull([pull])
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Get or set the pin pull state.
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See the constructor documentation for details of the ``pull`` argument.
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Availability: cc3200, stm32 ports.
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.. method:: Pin.drive([drive])
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Get or set the pin drive strength.
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See the constructor documentation for details of the ``drive`` argument.
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Availability: cc3200 port.
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Constants
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---------
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The following constants are used to configure the pin objects. Note that
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not all constants are available on all ports.
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.. data:: Pin.IN
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Pin.OUT
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Pin.OPEN_DRAIN
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Pin.ALT
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Pin.ALT_OPEN_DRAIN
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Pin.ANALOG
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Selects the pin mode.
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.. data:: Pin.PULL_UP
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Pin.PULL_DOWN
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Pin.PULL_HOLD
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Selects whether there is a pull up/down resistor. Use the value
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``None`` for no pull.
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.. data:: Pin.DRIVE_0
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Pin.DRIVE_1
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Pin.DRIVE_2
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Selects the pin drive strength. A port may define additional drive
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constants with increasing number corresponding to increasing drive
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strength.
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.. data:: Pin.IRQ_FALLING
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Pin.IRQ_RISING
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Pin.IRQ_LOW_LEVEL
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Pin.IRQ_HIGH_LEVEL
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Selects the IRQ trigger type.
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