Merge branch 'master' into debug-serialusb.

Chose debug-serialusb version in cases of conflict.

Conflicts:
	libmaple/usb/usb_callbacks.c

1 files changed, 68 insertions, 0 deletions

diff --git a/docs/source/lang/api/digitalwrite.rst b/docs/source/lang/api/digitalwrite.rst
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+.. highlight:: cpp
+
+.. _lang-digitalwrite:
+
+digitalWrite()
+==============
+
+Write a :ref:`HIGH <lang-constants-high>` or a :ref:`LOW
+<lang-constants-low>` value to a pin configured as :ref:`OUTPUT
+<lang-constants-output>`.
+
+Library Documentation
+---------------------
+
+.. doxygenfunction:: digitalWrite
+
+Discussion
+----------
+
+If the pin has been configured as an ``OUTPUT`` with :ref:`pinMode()
+<lang-pinmode>` its voltage will be set to the corresponding value:
+3.3V for ``HIGH``, and 0V (ground) for ``LOW``.
+
+.. TODO make the following paragraphs true, but refer the reader to
+.. INPUT_PULLUP and INPUT_PULLDOWN:
+
+If the pin is configured as an ``INPUT``, writing a ``HIGH`` value
+with ``digitalWrite()`` will enable an internal pullup resistor.
+Writing ``LOW`` will disable the pullup. The pullup resistor is enough
+to light an LED dimly, so if LEDs appear to work, but very dimly, this
+is a likely cause. The remedy is to set the pin to an output with the
+:ref:`pinMode() <lang-pinmode>` function.
+
+.. note:: Pin 13 is harder to use as an input than the other pins
+   because it has an LED and resistor soldered to it in series. If you
+   enable its internal pull-up resistor, it will likely hang at around
+   1.1V instead of the expected 3.3V because the onboard LED and
+   series resistor pull the voltage level down. If you must use pin 13
+   as a digital input, use an external pull-down resistor.
+
+Example
+-------
+
+The following example sets pin 13 to ``HIGH``, makes a one-second-long
+delay, sets the pin back to ``LOW``, and delays again, causing a
+blinking pattern::
+
+
+    int ledPin = 13;                 // LED connected to digital pin 13
+
+    void setup() {
+      pinMode(ledPin, OUTPUT);      // sets the digital pin as output
+    }
+
+    void loop() {
+      digitalWrite(ledPin, HIGH);   // sets the LED on
+      delay(1000);                  // waits for a second
+      digitalWrite(ledPin, LOW);    // sets the LED off
+      delay(1000);                  // waits for a second
+    }
+
+See Also
+--------
+
+- :ref:`pinMode <lang-pinmode>`
+- :ref:`digitalRead <lang-digitalread>`
+
+.. include:: cc-attribution.txt