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DRV8711 Torque Register Settings

Costas Panagopoulos
Prodigy 20 points

I would like to ask,
if there is anyone that had programmed the TORQUE register bits SMPLTH bits above 011 value?

I am asking that because any time I try to program with a value bigger than 011 and read back the register bits, the SMPLTH MSB is 0.

  • 0
    TI__Guru** 114905 points

    Hi Costas,

    How are you reading the programming and reading the bits? Is it possible to capture both the write and read command on the scope for evaluation?

    Thanks.

  • 0 in reply to Rick Duncan
    Prodigy 20 points

    Hi Rick,

    I writting and reading the bits through microcontroller, and it is successfully for any other register in any bit combination.

    But with torque register the MSB bit is always trimmed, for example when I send the data 01xx xxxx xxxx and read the value from register, I reading 00xx xxxx xxxx.

    I do not exclude that may I have same glitch in SPI procedure, but it is not possible right now to capture the wave forms.

    Thanks.

  • 0 in reply to Costas Panagopoulos
    TI__Guru** 114905 points

    Hi Costas,

    It has been confirmed that the MSB will always read back as 0, regardless of the value written to it. The write of a 1 will be accepted and change the Back EMF threshold to the correct values, but will be read back as a 0.

    To compensate for this, using a shadow register ( a memory location  in the microcontroller containing the value written into the TORQUE register) is suggested. This shadow register mimics the actual register value. Using the shadow register and the read modify write technique will result in the desired operation, since the bit in the shadow register does toggle from 0 to 1. Another benefit of the shadow register is that the time to read the shadow is much faster since it does not require an SPI read operation.