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diff --git a/docs/source/lang/api/analogwrite.rst b/docs/source/lang/api/analogwrite.rst deleted file mode 100644 index 0169976..0000000 --- a/docs/source/lang/api/analogwrite.rst +++ /dev/null @@ -1,181 +0,0 @@ -.. highlight:: cpp - -.. _lang-analogwrite: - -.. _lang-api-analogwrite: - - -analogWrite() -============= - -analogWrite() is used to create a :ref:`PWM <pwm>` wave on a pin. - -.. note:: - - On the Maple, calling analogWrite() is the same as calling - :ref:`lang-pwmwrite`. We recommend writing pwmWrite() instead of - analogWrite(). - - This is because PWM is not true analog output (it's not the output - of a `DAC - <http://en.wikipedia.org/wiki/Digital-to-analog_converter>`_\ ), so - the function is very badly named. For instance, **analogWrite() - has nothing to do with** :ref:`lang-analogread`\ , which can be - confusing. - - We provide analogWrite() for the sake of compatibility with Arduino - only. - -.. 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--65,535, 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 your board's :ref:`pin maps <gpio-pin-maps>` -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-hardwaretimer-interrupts>` 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, 14, 24, 27, and 28 or fifteen pins in total. That's *more* -PWM-capable pins as any Arduino board, but there are differences in -*which* pins support PWM. - -* 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. - -* **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, then any other 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 definitely requires Arduino's PWM frequency, then -the steps are: - -1. Figure out which :ref:`timer <lang-hardwaretimer>` controls PWM - output on your pin (\ :ref:`your board's Timer Pin Map - <gpio-pin-maps>` is your friend here). - -2. Let's say it's timer ``n``, where ``n`` is some number. You'll - then need to put "``HardwareTimer timer(n);``" with your variables, - as described in the :ref:`HardwareTimer - <lang-hardwaretimer-getting-started>` reference. - -3. In your :ref:`lang-setup`, put "``timer.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. The important examples are :ref:`timer interrupts -<lang-hardwaretimer-interrupts>` and :ref:`PWM -<timers-pwm-conflicts>`\ . - -See Also --------- - -- :ref:`pwm` -- :ref:`lang-pwmwrite` -- :ref:`BOARD_NR_PWM_PINS <lang-board-values-nr-pwm-pins>` -- :ref:`boardPWMPins <lang-board-values-pwm-pins>` - -.. 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:: /arduino-cc-attribution.txt |