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.. _gpio:
GPIO
====
Each LeafLabs board comes with ready-to-use General Purpose
Input/Output (GPIO) pins, which are numbered starting from zero.
These numbers are listed on your board's silkscreen, next to where the
pin is broken out to a header. Many pins may additionally be used for
special features or interfacing with other hardware.
.. contents:: Contents
:local:
.. _gpio-modes:
GPIO Modes
----------
Each GPIO pin can be configured using :ref:`lang-pinmode` to behave in
a number of ways: as a digital output pin, as an analog input pin,
etc.
A :ref:`WiringPinMode <lang-pinmode-wiringpinmode>` value specifies
the complete set of possible configurations; not every pin can have
all of these modes. For example, on the Maple, pin 15 may have mode
``INPUT_ANALOG``, but not ``PWM``. See your board's :ref:`pin maps
<gpio-pin-maps>` and its silkscreen for more information on what
functionality is available on each pin.
Function Reference
------------------
- :ref:`lang-pinmode`
- :ref:`lang-digitalread`
- :ref:`lang-digitalwrite`
- :ref:`lang-analogread`
- :ref:`lang-pwmwrite` (Maple's equivalent to ``analogWrite()``; see
:ref:`lang-analogwrite` for differences from the Arduino version).
.. _gpio-ports:
GPIO Ports
----------
Normally, you'll interact with pins using just their number (or a
constant like :ref:`BOARD_LED_PIN <lang-board-values-led>` which
stands for a number). However, behind the scenes, the STM32
microcontroller on your board separates the pins into groups called
*GPIO ports*. Each GPIO port is given a letter, so for example,
there's GPIO port A, port B, and so on\ [#fnumports]_. The pins on a
GPIO port are given *bit numbers*, which go from 0 to 15. In ST's
documentation, a pin is given by the letter "P", followed by its port
letter and bit number. For instance, "PA4" is GPIO port A, bit 4.
.. _gpio-pin-maps:
Pin Maps
--------
Part of the library's job is to convert normal pin numbers
into the corresponding GPIO port and bit when you call functions like
:ref:`lang-pinmode`. It does this using a *pin map*, which lists the
GPIO port and bit for each pin number. The GPIO documentation for
your board includes its pin map, which also lists the other
peripherals by pin number:
* `Leaflabs Maple`_
* `Leaflabs Maple RET6`_
* `Leaflabs Maple Mini`_
* `Leaflabs Maple Native Beta`_
.. _gpio-5v-tolerant:
The current and voltage limitations were determined using the STM32
datasheets. In particular, only some GPIO pins are **5V tolerant**,
which means that applying 5 volts to a pin and reading it as input or
allowing it to drain to ground will not damage that pin. Connecting a
voltage higher than 3.3V to a non-5V tolerant pin may damage your
board.
.. _gpio-recommended-reading:
Recommended Reading
-------------------
* ST Documentation for the STM32F103 series of microcontrollers:
* `Reference Manual RM0008
<http://www.st.com/web/en/resource/technical/document/reference_manual/CD00171190.pdf>`_
(PDF); general, definitive resource for STM32F1 line.
* `Programming Manual PM0056
<http://www.st.com/st-web-ui/static/active/en/resource/technical/document/programming_manual/CD00228163.pdf>`_
(PDF); assembly language and register reference.
.. rubric:: Footnotes
.. [#fnumports] The total number of GPIO ports depends on what board
you have. For example, Maple Mini has three: ports A, B, and C.
Maple Native has seven: ports A through G.
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