Warning:

To protect the digital assets of creators and enhance system security and stability, the CyberBrick Multi-Function Core Board does not support firmware flashing with any third-party tools! If you need to restore the Multi-Function Core Board to its factory state, please wait for the official recovery tool to be released by CyberBrick. If you proceed to flash the firmware using third-party tools, the firmware of the Multi-Function Core Board will be permanently damaged and cannot be recovered. CyberBrick will not be responsible for any consequences resulting from such operations.

This documentation is adapted from the official MicroPython project. The CyberBrick team has extended the source code with custom interfaces and features to our hardware and application needs.

In addition to these enhancements, certain built-in MicroPython interfaces have been intentionally disabled to protect the system's integrity, and ensure the overall security and reliability of the device. This also facilitates content protection for creators' intellectual property, where applicable.

Portions of the content are derived from the official MicroPython documentation and have been included here under its open-source license to provide users with a consistent and enriched development experience tailored to the CyberBrick platform.

class PWM – pulse width modulation

This class provides pulse width modulation output.

Example usage:

from machine import PWM

pwm = PWM(pin, freq=50, duty_u16=8192)  # create a PWM object on a pin
                                        # and set freq and duty
pwm.duty_u16(32768)     # set duty to 50%

# reinitialise with a period of 200us, duty of 5us
pwm.init(freq=5000, duty_ns=5000)

pwm.duty_ns(3000)       # set pulse width to 3us

pwm.deinit()

Constructors

class machine.PWM(dest, *, freq, duty_u16, duty_ns, invert)

Construct and return a new PWM object using the following parameters:

  • dest is the entity on which the PWM is output, which is usually a machine.Pin object, but a port may allow other values, like integers.

  • freq should be an integer which sets the frequency in Hz for the PWM cycle.

  • duty_u16 sets the duty cycle as a ratio duty_u16 / 65535.

  • duty_ns sets the pulse width in nanoseconds.

  • invert inverts the respective output if the value is True

Setting freq may affect other PWM objects if the objects share the same underlying PWM generator (this is hardware specific). Only one of duty_u16 and duty_ns should be specified at a time. invert is not available at all ports.

Methods

PWM.init(*, freq, duty_u16, duty_ns)

Modify settings for the PWM object. See the above constructor for details about the parameters.

PWM.deinit()

Disable the PWM output.

PWM.freq([value])

Get or set the current frequency of the PWM output.

With no arguments the frequency in Hz is returned.

With a single value argument the frequency is set to that value in Hz. The method may raise a ValueError if the frequency is outside the valid range.

PWM.duty_u16([value])

Get or set the current duty cycle of the PWM output, as an unsigned 16-bit value in the range 0 to 65535 inclusive.

With no arguments the duty cycle is returned.

With a single value argument the duty cycle is set to that value, measured as the ratio value / 65535.

PWM.duty_ns([value])

Get or set the current pulse width of the PWM output, as a value in nanoseconds.

With no arguments the pulse width in nanoseconds is returned.

With a single value argument the pulse width is set to that value.

Limitations of PWM

  • Not all frequencies can be generated with absolute accuracy due to the discrete nature of the computing hardware. Typically the PWM frequency is obtained by dividing some integer base frequency by an integer divider. For example, if the base frequency is 80MHz and the required PWM frequency is 300kHz the divider must be a non-integer number 80000000 / 300000 = 266.67. After rounding the divider is set to 267 and the PWM frequency will be 80000000 / 267 = 299625.5 Hz, not 300kHz. If the divider is set to 266 then the PWM frequency will be 80000000 / 266 = 300751.9 Hz, but again not 300kHz.

    Some ports like the RP2040 one use a fractional divider, which allow a finer granularity of the frequency at higher frequencies by switching the PWM pulse duration between two adjacent values, such that the resulting average frequency is more close to the intended one, at the cost of spectral purity.

  • The duty cycle has the same discrete nature and its absolute accuracy is not achievable. On most hardware platforms the duty will be applied at the next frequency period. Therefore, you should wait more than “1/frequency” before measuring the duty.

  • The frequency and the duty cycle resolution are usually interdependent. The higher the PWM frequency the lower the duty resolution which is available, and vice versa. For example, a 300kHz PWM frequency can have a duty cycle resolution of 8 bit, not 16-bit as may be expected. In this case, the lowest 8 bits of duty_u16 are insignificant. So:

    pwm=PWM(Pin(13), freq=300_000, duty_u16=2**16//2)

    and:

    pwm=PWM(Pin(13), freq=300_000, duty_u16=2**16//2 + 255)

    will generate PWM with the same 50% duty cycle.