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Diffstat (limited to 'docs/source/pwm.rst')
| -rw-r--r-- | docs/source/pwm.rst | 49 |
1 files changed, 36 insertions, 13 deletions
diff --git a/docs/source/pwm.rst b/docs/source/pwm.rst index 178d103..fd72842 100644 --- a/docs/source/pwm.rst +++ b/docs/source/pwm.rst @@ -1,10 +1,9 @@ .. _pwm: -============================== - Pulse-Width Modulation (PWM) -============================== +PWM +=== -Pulse Width Modulation is a basic technique to create repeated square +Pulse Width Modulation (PWM) is a basic technique to create repeated square waves (digital high/low voltage transitions) of user defined length and duty cycle. It can be used as a way to encode an "analog" signal on a single digital (high/low) line using the time between transitions @@ -42,7 +41,7 @@ to track down exactly which timer *channel* corresponds to each pin. Timer1 | D6,D7,D8 Timer2 | D0,D1,D2,D3 Timer3 | D11,D12,D27,D28 - Timer4 | D5,D9,D14,D24 + Timer4 | D5,D9,D14,D24 Background ---------- @@ -96,11 +95,11 @@ Function Reference ``pinMode(pin_num, PWM)`` - This command is usually called from `setup()`_ to tell the - microcontroller that pin_num should be configured to PWM - output. ``PWM`` implies regular driven OUTPUT; ``PWM_OPEN_DRAIN`` is - also available (see the list of :ref:`GPIO modes <gpio-modes>` for - more information). + This command is usually called from :ref:`setup() <lang-setup>` to + tell the microcontroller that pin_num should be configured to PWM + output. ``PWM`` implies regular driven OUTPUT; ``PWM_OPEN_DRAIN`` + is also available (see the list of :ref:`GPIO modes <gpio-modes>` + for more information). .. _pwm-pwmwrite: @@ -114,7 +113,7 @@ Function Reference .. _pwm-overflow: -``Timer1.setOverflow(overflow)`` +``Timer[1,2,3,4].setOverflow(overflow)`` This function sets the period ("reload" or "overflow") value for an entire PWM timer bank. The value is 16bit (0 to 65535) and @@ -144,8 +143,32 @@ Function Reference For instance, an 8MHz frequency can be achieved by setting ``prescale`` to 9, since 72MHz / 9 = 8MHz. - This function is normally called once from, `setup()`_, but the - timer can be reconfigured with a new prescaler at any time. + This function is normally called once from, :ref:`lang-setup`, but + the timer can be reconfigured with a new prescaler at any time. + + * Configure the prescaler and overflow values to generate a timer + * reload with a period as close to the given number of + * microseconds as possible. + * + * The return value is the overflow, which may be used to set + * channel compare values. However, if a clock that fires an + * interrupt every given number of microseconds is all that is + * desired, and the relative "phases" are unimportant, channel + * compare values may all be set to 1. + +``Timer[1,2,3,4].setPeriod(period_in_microseconds)`` + + Configure the prescaler and overflow values to generate a timer + reload with a period as close to the given number of microseconds + as possible. + + The return value is the overflow, which may be used to set channel + compare values. However, if a clock that fires an interrupt every + given number of microseconds is all that is desired, and the + relative "phases" are unimportant, channel compare values may all + be set to 1. + + Recommended Reading ------------------- |