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diff --git a/source/lang/analogwrite.rst b/source/lang/analogwrite.rst deleted file mode 100644 index 2c50a42..0000000 --- a/source/lang/analogwrite.rst +++ /dev/null @@ -1,166 +0,0 @@ -.. highlight:: cpp - -.. _lang-analogwrite: - -analogWrite() -============= - -.. note:: - - On the Maple, calling analogWrite() is the same as calling - :ref:`lang-pwmwrite`\ ; see that function's documentation for more - information. - - This is because PWM is not true analog output (i.e., is not the - output of a `DAC - <http://en.wikipedia.org/wiki/Digital-to-analog_converter>`_\ ), so - the function is badly named. For instance, **analogWrite() has - absolutely nothing to do with** :ref:`lang-analogread`\ , which is - potentially confusing. - - The alias of analogWrite() to pwmWrite() is provided (sigh) for the - sake of compatibility with Arduino, but we recommend using - :ref:`lang-pwmwrite` when writing new software, for clarity. - -.. contents:: Contents - :local: - -.. _lang-analogwrite-compatibility: - -Arduino Compatibility ---------------------- - -There are a few important differences between Arduino's `analogWrite() -<http://arduino.cc/en/Reference/AnalogWrite>`_ and Maple's -:ref:`lang-pwmwrite` that you should keep in mind. In each case, we -have some recommendations you can use to help converting from Arduino -to Maple. - -Difference 1: Duty cycle range is different -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -The first and most important difference is that the largest possible -value for the duty cycle is much bigger on the Maple. Using Arduino's -analogWrite(), the duty cycle ranges between 0--255 (always off -- -always on)\ [#fbytemax]_\ . Using Maple's pwmWrite(), the duty cycle -ranges from 0--65,535 by default\ [#fuint16max]_\ . - -This is a good thing! The greater range of values on the Maple gives -you much more precise control over the duty cycle of your PWM output. - -If you're porting code from the Arduino and want a quick-and-dirty -fix, one solution is to :ref:`map <lang-map>` the argument to -analogWrite into the right range:: - - // Arduino code: - analogWrite(pin, duty); - - // Becomes Maple code: - analogWrite(pin, map(duty, 0, 255, 0, 65535)); - -This will convert values in the range 0-255 to values in the range -0--65,635, which is the correct default range for all of the timers -which control PWM output. See the :ref:`timers reference <timers>` -for more information. - -Another fix is to consult the :ref:`pin mapping mega table -<pin-mapping-mega-table>` to find the timer which controls PWM on the -pin you're using, then set that Timer's overflow to 255. Subsequent -calls to analogWrite() should work as on the Arduino (with the same -loss of precision). Note, however, that that affects the overflow for -the **entire timer**, so other code relying on that timer (such as any -:ref:`interrupts <lang-attachinterrupt>` the timer controls) will -likely need to be modified as well. - -Difference 2: You must use pinMode() to set up PWM -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -The second difference is that on the Maple, you **must** set up the pin -for PWM output using :ref:`lang-pinmode`\ , with argument ``PWM``. -This should just be one extra line of code in your -:ref:`lang-setup` function. Example:: - - void setup() { - // set up pin 9 for PWM - pinMode(9, PWM); - } - -This also means that you can't later call :ref:`lang-digitalread` -or :ref:`lang-digitalwrite` on that pin (unless some time in -between, you use pinMode() to reconfigure that pin for ``INPUT`` or -``OUTPUT``; see the :ref:`lang-pinmode` page for more information). - -Difference 3: No PWM on pin 10 -^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -On the Maple, the pins which support PWM are: 0, 1, 2, 3, 5, 6, 7, 8, -9, 11, 12, and 14, or twelve pins in total. That is at least as -*many* PWM pins as any Arduino board, but there are differences in -*which* pins support it. - -* On **most Arduino boards** (those with the ATmega168 or ATmega328; - this includes the **Arduino Uno**), this function works on pins 3, - 5, 6, 9, 10, and 11, or six pins total. Note that these boards - support PWM on pin 10, while Maple does not. - -* On the **Arduino Mega**, PWM works on pins 2 through 13, or twelve pins - total. Note that this board supports PWM on pins 4, 10, and 13, - while the Maple does not. Maple supports PWM on pins 0, 1, and 14, - which the Mega does not, making the total number of pins supporting - PWM equal on these boards. - -* **Older Arduino boards** with an ATmega8 only support analogWrite() on - pins 9, 10, and 11. Maple does not support PWM on pin 10. - -In all cases, Arduino boards support PWM on pin 10, unlike Maple. We -did our best to make PWM as pin-compatible as possible; however, -circuit layout constraints prevented us from achieving perfect -compatibility. - -The "safest" pins to use for PWM output are pins 9 and 11. These pins -work on any Arduino board and on Maple. The "safe" pins, which work -on most recent Arduino boards, the Arduino Mega and the Maple, are -pins 3, 5, 6, 9, and 11. Thus, if you want your project to be as -portable as possible between Maple and Arduino, we recommend using the -"safest" pins first, then the "safe" pins, as necessary. - -Difference 4: PWM frequency -^^^^^^^^^^^^^^^^^^^^^^^^^^^ - -The frequency of the PWM signal (i.e., the frequency of a complete -on/off cycle) on the Arduino is approximately 490 Hz. - -On the Maple, the frequency is configurable, defaulting to about 1100 -Hz, or 1.1 KHz. This is because the PWM frequency is the frequency of -the timer which controls PWM output on the particular pin (\ -:ref:`the PWM tutorial has the details <pwm>`\ ). - -If your application absolutely requires Arduino's PWM frequency (it -probably doesn't), then the steps are: - -1. Figure out which timer controls PWM output on your pin (\ :ref:`this table <pwm-timer-table>` is your friend here). Let's say it's ``Timern``\ , where ``n`` is some number 1, 2, 3, or 4. - -2. Call ``Timern.setPeriod(2041)``\ . This will set the timer's period to approximately 2041 microseconds, which is a frequency of approximately 490 Hz. - -Be aware that this will change the period for the **entire timer**\ , -and will affect anything else in your program that depends on that -timer. One example is :ref:`interrupts <timers-attachinterrupt>`\ . -You've been :ref:`warned <timers-pwm-conflicts>`\ . - -See also --------- - -- :ref:`Maple PWM tutorial <pwm>` - -.. rubric:: Footnotes - -.. [#fbytemax] This is because the value for the duty cycle on Arduino - must fit in 1 byte of memory, and an unsigned (i.e., nonnegative) - integer with size 1 byte can hold the values between 0 and 255. - -.. [#fuint16max] This is because the value for the duty cycle on the - Maple uses 2 bytes of memory, and an unsigned (i.e., nonnegative) - integer with size 2 bytes can hold the values between 0 and 65,535. - - -.. include:: cc-attribution.txt |