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+.. highlight:: cpp
+
+.. _lang-analogread:
+
+.. _lang-api-analogread:
+
+analogRead()
+============
+
+Used to perform ADC conversion.
+
+.. contents:: Contents
+   :local:
+
+Library Documentation
+---------------------
+
+.. doxygenfunction:: analogRead
+
+Discussion
+----------
+
+Reads the value from the specified analog pin.  The Maple board
+contains a 16-channel, 12-bit analog to digital converter.  This means
+that it will map input voltages between 0 and 3.3 volts into integer
+values between 0 and 4095.  This yields a resolution between readings
+of 3.3V / 4096 units, or 0.8 millivolts.  However, a number of factors
+interfere with getting full accuracy and precision.  For more
+information, see :ref:`adc`.
+
+Before calling analogRead() on a pin, that pin must first be
+configured for analog input, using :ref:`lang-pinMode` (you only
+have to do this once, so it's usually done in :ref:`lang-setup`\ ).
+
+It takes about 0.8 microseconds (.0000008 seconds) to read an analog
+input, so the maximum sample rate using this function is approximately
+1.3 million samples per second\ [#fsamp]_.
+
+
+Parameter Discussion
+--------------------
+
+The pin parameter is the number of the analog input pin to read from.
+Header pins on the Maple with ADC functionality (marked as "AIN" on
+the silkscreen) are:
+
+  0, 1, 2, 3, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 27, 28
+
+Note that pins 3, 27, and 28 are not marked AIN on the silkscreen
+for Maple revisions through Rev 5, however, they **do work** as
+analog input pins.
+
+Note
+----
+
+If the analog input pin is not connected to anything, the value
+returned by analogRead() will fluctuate based on a number of factors
+(e.g. the values of the other analog inputs, how close your hand is to
+the board, etc.) in a seemingly random way.
+
+
+Example
+-------
+
+ ::
+
+
+    int analogPin = 3;     // potentiometer wiper (middle terminal) connected
+                           // to analog pin 3. outside leads to ground and +3.3V
+    int val = 0;           // variable to store the value read
+
+    void setup() {
+      pinMode(analogPin, INPUT_ANALOG); // set up pin for analog input
+      SerialUSB.begin();                // set up usb virtual COM port
+    }
+
+    void loop() {
+      val = analogRead(analogPin);    // read the input pin
+      SerialUSB.println(val);         // print the value, for debugging with
+                                      // a serial monitor
+    }
+
+
+Arduino Compatibility
+---------------------
+
+The Arduino board contains a 6 channel (8 channels on the Mini and
+Nano, 16 on the Mega), 10-bit analog to digital converter with an
+input voltage range of 0V--5V. This means that it will map input
+voltages between 0 and 5 volts (which is **larger** than Maple's range
+of 0V-3.3V) into integer values between 0 and 1023 (which is
+**smaller** than the Maple's range of 0--4095).
+
+This yields a theoretical resolution between readings of: 5 volts /
+1024 units or .0049 volts (4.9 mV) per unit on Arduino boards, which
+is larger, and thus less precise, than Maple's 0.0008 volts (0.8 mV).
+
+If your program expects Arduino-style 10-bit ADC, you can :ref:`right
+shift <lang-bitshift>` the value of a Maple readout by 2, like so::
+
+    // right shift means that the result will be between 0 and 1023;
+    // be aware that you're losing a lot of precision if you do this
+    int adc_reading = analogRead(pin) >> 2;
+
+On the Arduino, the input range and resolution can be changed using
+their implementation of `analogReference()
+<http://arduino.cc/en/Reference/AnalogReference>`_\ . Because of the
+way its hardware (as of Rev 5) was designed, it's not possible to
+implement analogReference on the Maple, so this function doesn't
+exist.  If your inputs lie in a different voltage range than 0V--3.3V,
+you'll need to bring them into that range before using analogRead.
+Some basic tools to accomplish this are `resistor dividers
+<http://en.wikipedia.org/wiki/Voltage_divider>`_ and `Zener diodes
+<http://en.wikipedia.org/wiki/Voltage_source#Zener_voltage_source>`_\
+. However, opamps and other powered components can also be used if
+greater precision is required.
+
+Finally, On the Arduino, it takes significantly longer to read analog
+input: about 100 microseconds (0.0001 s), so the maximum reading rate
+is 10,000 times a second.
+
+
+See also
+--------
+
+- :ref:`ADC note <adc>`
+- `(Arduino) Tutorial: Analog Input Pins <http://arduino.cc/en/Tutorial/AnalogInputPins>`_
+
+
+.. rubric:: Footnotes
+
+.. [#fsamp] This is based on the current configuration of a 55.5 cycle
+   sample time, at 72 MHz. However, the minimum sample time *possible*
+   is 1.5 cycles, leading to a theoretical maximum of approximately 48
+   million samples per second (of course, doing anything with the
+   readings also consumes cycles, so this maximum can't be reached in
+   practice).
+
+   See the `STM32 Reference Manual <full-manual>`_, §§11.12.4--5
+   (pp. 225--226), for more information on the low-level bit twiddling
+   currently necessary to change the sample time.  For examples of how
+   the ADCs are configured in libmaple, see `adc.h
+   <http://github.com/leaflabs/libmaple/blob/master/libmaple/adc.h>`_
+   and `adc.c
+   <http://github.com/leaflabs/libmaple/blob/master/libmaple/adc.c>`_\
+   .  Be aware that changing the sample time has important
+   consequences related to the impedance of the device connected to
+   the input pin.  If you want to make changes, as a minimum, you
+   should first read ST's application notes on `ADC modes
+   <stm32-adc-modes>`_ and `ADC oversampling
+   <stm32-adc-oversampling>`_.
+
+
+.. include:: cc-attribution.txt