76 lines
2.4 KiB
ReStructuredText
76 lines
2.4 KiB
ReStructuredText
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GPIO Pins
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=========
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The way to connect your board to the external world, and control other
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components, is through the GPIO pins. Not all pins are available to use,
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in most cases only pins 0, 2, 4, 5, 12, 13, 14, 15, and 16 can be used.
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The pins are available in the machine module, so make sure you import that
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first. Then you can create a pin using::
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>>> pin = machine.Pin(0)
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Here, the "0" is the pin that you want to access. Usually you want to
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configure the pin to be input or output, and you do this when constructing
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it. To make an input pin use::
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>>> pin = machine.Pin(0, machine.Pin.OUT, machine.Pin.PULL_UP)
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You can either use PULL_UP or PULL_NONE for the input pull-mode. If it's
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not specified then it defaults to PULL_NONE. You can read the value on
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the pin using::
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>>> pin.value()
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0
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The pin on your board may return 0 or 1 here, depending on what it's connected
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to. To make an output pin use::
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>>> pin = machine.Pin(0, machine.Pin.OUT)
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Then set its value using::
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>>> pin.value(0)
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>>> pin.value(1)
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Or::
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>>> pin.low()
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>>> pin.high()
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External interrupts
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-------------------
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All pins except number 16 can be configured to trigger a hard interrupt if their
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input changes. You can set code (a callback function) to be executed on the
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trigger.
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Let's first define a callback function, which must take a single argument,
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being the pin that triggered the function. We will make the function just print
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the pin::
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>>> def callback(p):
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... print('pin change', p)
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Next we will create two pins and configure them as inputs::
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>>> from machine import Pin
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>>> p0 = Pin(0, Pin.IN)
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>>> p2 = Pin(2, Pin.IN)
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An finally we need to tell the pins when to trigger, and the function to call
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when they detect an event::
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>>> p0.irq(Pin.IRQ_FALLING, callback)
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>>> p2.irq(Pin.IRQ_RISING | Pin.IRQ_FALLING, callback)
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We set pin 0 to trigger only on a falling edge of the input (when it goes from
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high to low), and set pin 2 to trigger on both a rising and falling edge. After
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entering this code you can apply high and low voltages to pins 0 and 2 to see
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the interrupt being executed.
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A hard interrupt will trigger as soon as the event occurs and will interrupt any
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running code, including Python code. As such your callback functions are
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limited in what they can do (they cannot allocate memory, for example) and
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should be as short and simple as possible.
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