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DRV8711: total SPI interface

DavidVescovi
Genius 5470 points

Part Number: DRV8711

I have an microcontroller interface that has limited GPIO pins but does have a SPI interface.

Is it possible to use the DRV8711 in a "totally SPI" interface mode?

I see in the register map the CTRL register has a RDIR and a RSTEP bit.. Am I correct in assuming these bits can mimic the same as the DIR and STEP physical pins?

I.E. I can leave the physical STEP and DIR pins unconnected and just use the CTRL register bits to operate the stepper?

  • 0
    TI__Guru 56650 points

    David,

    If the motor runs with a super low speed (RSTEP SPI command is not very busy),  leave the physical STEP and DIR pins unconnected and just use the CTRL register bits to operate the stepper.

    If the motor speed is high, the SPI RSTEP signal is hard to keep on a same frequency to get a smooth motion.   

  • 0 in reply to Wang5577
    Genius 5470 points

    The SPI interface can run up to 4MHZ. The SPI software is running on a multithreadded OS.

    The application is a simple 360 degree positional stepper.

    My question was more to the point is if this is a proper use of the part and if I am interpreting the RSTEP and RDIR bit definition correctly?

     

  • 0 in reply to DavidVescovi
    TI__Guru 56650 points

    David,

    If you can always give RSTEP constant update rate at the highest motor speed and your highest micro-stepping setting, this is a proper use of the part.

  • 0 in reply to Wang5577
    TI__Mastermind 37683 points

    David,

    Adding to Wang's comment, the datasheet states in section 7.3.2 "At each rising edge of the STEP input, or each time a 1 is written to the RSTEP bit in the CTRL register, the indexer travels to the next state in the table. The direction is shown with the DIR pin high and the RDIR bit in the CTRL register set to 0, or the DIR pin low and the RDIR bit set to 1. If the DIR pin is low with the RDIR bit 0, or the DIR pin is high with the RDIR bit 1, the sequence is reversed. Positive current is defined as xOUT1 = positive with respect to xOUT2." 

    So if you plan on leaving the DIR pin open (pulled down to 0V internally), the RDIR bit should be set to 1 to follow the step sequence in Table 4. Changing RDIR to 0 will reverse the step sequence.