• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 81 subscribers
  • Views 510 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMS320F28069 CAP1, 2 and 3 on GPIO40, 41 and 42

Maxime Torrelli
Intellectual 610 points

Other Parts Discussed in Thread: DRV8301, CONTROLSUITE

Hello,

In the linked document we can see (sheet on 7) that signals CAP1, CAP2 and CAP3 are connected respectively to GPIO40, 41 and 42. 

First question: is this connector made to connect a rotary position sensor returning 3 pulsed signals?

Second question: If so, why isn't it connected to a CAP or a HRCAP GPIO?

Thanks for your helpDRV8301-KIT_Schematics.PDF

  • 0
    TI__Guru 57255 points

    Hi Maxime,

    The CAP1-3 signals are mainly there to enable a user to connect something like hall-effect sensors to the board.

    There are several things that, when combined, have led to what you have described:

    1. The DRV8301 baseboard is designed to work with several different controlCARDs (namely the F28069 and the F28035).  The controlCARD pinout helps with compatibility from controlCARD to controlCARD, but there is a limit - different controlCARDs hold different devices which have different amount of pins and peripherals.
      1. The most compatible place for eCAP from controlCARD-to-controlCARD is GPIO24-27, which also is a place where SPI is common - and we needed to have SPI.  I don't have a complete understanding of why every peripheral was chosen where it was on the controlCARD connector, however TI had to think about this during design.
      2. HRCAP placement in the GPIO mux was not consistent between F28035 and F28069.

    2. For Hall-effect sensors, you can generally get away with polling them inside the motor control interrupt to determine the state (and therefore help find the commutation state in BLDC control, for instance).  Getting the speed information, which the eCAP/HRCAP would help us get, was judged to be not too important on this specific kit.

    Bullet 1 describes things that TI had to work around because the board was meant to be generic.  For a custom design, the full flexibility of the GPIO mux can be utilized.

    Hopefully this helps!


    Thank you,
    Brett

  • 0 in reply to Brett Larimore
    Intellectual 610 points
    Thanks for your help.

    You mean that in order to get the position information from a Hall-effect sensor I do not need to connect it to a eCAP or HRCAP pin? The Interrupt system is enough to get the position information?

    Regards,
  • 0 in reply to Maxime Torrelli
    TI__Guru 57255 points

    Hi Maxime,

    In several of TI's motor control software examples, we took the approach of configuring these pins as standard GPIO inputs.  We then read whether each of the 3 GPIOs are high or low inside the motor control ISR (the only ISR in the system).  The thought here is that you only need the new position to determine the way you want the next period of PWM outputs to be configured, so we can read the position here.  An example of what I've described is the following:
    \controlSUITE\development_kits\HVMotorCtrl+PfcKit_v2.1\HVBLDC_Sensored\

    A different approach may be to configure the 3 hall-effect pins as eCAP and then have the eCAP generate interrupts on transitions.  In the generated interrupts you could then determine the new "position".  (a similar thing could be done by configuring the GPIO as external interrupt sources if someone didn't want to use eCAPs)

    Either way, the eCAP can still be useful in determining the speed of the shaft by looking at the hall-effect transitions.

    You will need to determine what method is best for your application.


    Thank you,
    Brett