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MCF8329A: How to set reference speed in I2C speed mode

?? ?
Prodigy 70 points
Part Number: MCF8329A

Tool/software:

I want to control the motor speed using I2C speed mode, but it seems that entering the speed value in the DIGITAL_SPEED_CTRL register has no effect. Also, it is mentioned that entering values via I2C while the motor is running is not possible. I’m curious how to input values in I2C mode.

  • +1
    TI__Expert 6011 points

    Hi,

    Thanks for your question, have you set the  SPEED_MODE to 10b? If not set speed control through I2C is not possible.

    Regards,

    Sachin S

  • +1 in reply to Sachin S
    Prodigy 70 points

    "I'm really sorry. Upon checking, I found that the WAKE/SPEED pin was pulled up, which kept it in standby mode. It's working well now. However, I have a few more questions.

    1. We are currently trying to set the MAX_SPEED, but our motor has 3 pole pairs and we want to run it at 3000 RPM. The calculation shows it expressed in Hz, but does that ultimately refer to RPS (Revolutions Per Second)? If so, would the calculation be 3000 x 3 (pole pairs) / 60 (RPM to Hz) = 150? Therefore, when calculating for MAX_SPEED, would I set it to 150 / 6 = 25?" Thank you.
  • +1 in reply to ?? ?
    TI__Expert 6011 points

    Hi,

    The relation between the electrical speed (f, in Hz) and the rotational speed (RPM, in RPM) is as follows:

    f = RPM x (number of pole pairs)/60

    So given your values, 

    f = 150Hz, you can set this as the maximum speed.

    Thanks and regards,

    Sachin S