Possibly documentation error for pwm_write?

[dshaw619]

The docstring for pwm_write show on https://mryslab.github.io/pymata4/device_writes/ says ":param value: Pin value (0 - 0x4000)", but then the Notes say "The value parameter is typically set between 0 and 255" which would be 0 - 0xff wouldn't it?

[MrYsLab]

Thanks for your question.

The comment is actually correct. Typically, one uses a value between 0 and 255, but the Arduino low-level library has a little known feature to control the PWM clock rate by setting the upper order bits. For some reason, the original authors of StandardFirmata decided to support this feature. I have never used it, nor have I seen it used.

The feature is documented on the Arduino site here. I find this documentation somewhat confusing and found that this article is easier to understand. The Firmata implementation supports 14 bits. I am not sure why not the full 16, but that is the reason for value 0x4000.

I am closing the issue, but if you have any additional comments or questions, you may post them here and I will see them.

[dshaw619]

Thanks for the explanation.

Doug

On Sat, Jun 27, 2020 at 6:28 AM Alan Yorinks notifications@github.com wrote:

Thanks for your question.

The comment is actually correct. Typically, one uses a value between 0 and 255, but the Arduino low-level library has a little known feature to control the PWM clock rate by setting the upper order bits. For some reason, the original authors of StandardFirmata decided to support this feature. I have never used it, nor have I seen it used.

The feature is documented on the Arduino site here https://www.arduino.cc/en/Tutorial/SecretsOfArduinoPWM. I find this documentation somewhat confusing and found that this article https://www.arduinoslovakia.eu/blog/2017/7/16-bitove-rozlisenie-pwm-pre-arduino?lang=enis easier to understand. The Firmata implementation supports 14 bits. I am not sure why not the full 16, but that is the reason for value 0x4000.

I am closing the issue, but if you have any additional comments or questions, you may post them here and I will see them.

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