# 5.2.1.4 Pin

A pin is the basic object to control I/O pins \(also known as GPIO - general-purpose input/output\). 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.

## Quick Usage Example

```python
from machine import Pin

# initialize `P9` in gpio mode and make it an output
p_out = Pin('P9', mode=Pin.OUT)
p_out.value(1)
p_out.value(0)
p_out.toggle()
p_out(True)

# make `P10` an input with the pull-up enabled
p_in = Pin('P10', mode=Pin.IN, pull=Pin.PULL_UP)
p_in() # get value, 0 or 1
```

## Constructors

### class machine.Pin\(id, ...\)

Create a new Pin object associated with the string `id`. If additional arguments are given, they are used to initialise the pin. [See pin.init\(\)](pin.md#pin-init-mode-pull-alt)

```python
from machine import Pin
p = Pin('P10', mode=Pin.OUT, pull=None, alt=-1)
```

## Methods

### pin.init\(mode, pull, \* , alt\)

Initialise the pin:

* `mode` can be one of:
  * `Pin.IN` - input pin.
  * `Pin.OUT` - output pin in push-pull mode.
  * `Pin.OPEN_DRAIN` - input or output pin in open-drain mode.
* `pull` 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.
* `alt` is the id of the alternate function.

Returns: `None`.

### pin.id\(\)

Get the pin id.

### 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.

### pin\(\[value\]\)

Pin objects are callable. The call method provides a \(fast\) shortcut to set and get the value of the pin.

Example:

```python
from machine import Pin
pin = Pin('P12', mode=Pin.IN, pull=Pin.PULL_UP)
pin()   # fast method to get the value
```

See `pin.value()` for more details.

### pin.toggle\(\)

Toggle the value of the pin.

### pin.mode\(\[mode\]\)

Get or set the pin mode.

### pin.pull\(\[pull\]\)

Get or set the pin pull.

### pin.hold\(\[hold\]\)

Get or set the pin hold. You can apply a hold to a pin by passing `True` \(or clear it by passing `False`\). When a pin is held, its value cannot be changed by using `Pin.value()` or `Pin.toggle()` until the hold is released. This Can be used to retain the pin state through a core reset and system reset triggered by watchdog time-out or Deep-sleep events. Only pins in the RTC power domain can retain their value through deep sleep or reset.

These are: `P2, P3, P4, P6, P8, P9, P10, P13, P14, P15, P16, P17, P18, P19, P20, P21, P22, P23`

### pin.callback\(trigger, handler=None, arg=None\)

Set a callback to be triggered when the input level at the pin changes.

* `trigger` is the type of event that triggers the callback. 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.

The values can be OR-ed together, for instance `trigger=Pin.IRQ_FALLING | Pin.IRQ_RISING`

* `handler` is the function to be called when the event happens. This function will receive one argument. Set `handler` to `None` to disable it.
* `arg` is an optional argument to pass to the callback. If left empty or set to `None`, the function will receive the Pin object that triggered it.

Example:

```python
from machine import Pin

def pin_handler(arg):
    print("got an interrupt in pin %s" % (arg.id()))

p_in = Pin('P10', mode=Pin.IN, pull=Pin.PULL_UP)
p_in.callback(Pin.IRQ_FALLING | Pin.IRQ_RISING, pin_handler)
```

{% hint style="info" %}
For more information on how Pycom’s products handle interrupts, see [here](https://github.com/pycom/pycom-docs/tree/37661883902849b1a931ee273a23ae8e0f3d773e/chapter/toolsandfeatures/notes.md).
{% endhint %}

## Attributes

### class pin.exp\_board

Contains all Pin objects supported by the expansion board. Examples:

```python
Pin.exp_board.G16
led = Pin(Pin.exp_board.G16, mode=Pin.OUT)
Pin.exp_board.G16.id()
```

### class pin.module

Contains all `Pin` objects supported by the module. Examples:

```python
Pin.module.P9
led = Pin(Pin.module.P9, mode=Pin.OUT)
Pin.module.P9.id()
```

## Constants

The following constants are used to configure the pin objects. Note that not all constants are available on all ports.

* Selects the pin mode: `Pin.IN`, `Pin.OUT`, `Pin.OPEN_DRAIN`
* Enables the pull up or pull down resistor: `Pin.PULL_UP`, `Pin.PULL_DOWN`