MCF8315C-Q1: When it takes effect after I write RAM registers?

Part Number: MCF8315C-Q1
Other Parts Discussed in Thread: MCF8315C

Dear TI team:

     I have written to RAM register to change configure data, but it doesn't takes effect at the first motor start-up. While at the twice motor start-up, it works.

Why this occurs? And how i can make the register works at the first motor start-up after register writes?

The flow is a example to describe my operation steps:

   1) I write MOTOR_STARTUP1(84H) register by I2C communication, to configure ALIGN_TIME=1(=50 ms);

   2) I control the motor rotated and then stop.

   3) I write MOTOR_STARTUP1(84H) register, to configure ALIGN_TIME=2(=100 ms);

   4) I control the motor rotate, and measured the real align-time is 50 ms, not 100 ms. But I read back the MOTOR_STARTUP1(84H) register, which the ALIGN_TIME=2(=100 ms);

   5) I stopped the motor , and rotate it again. Now I measured the align-time is 100 ms.

  • Hi,

    I will reply to you by this week end. Are you using GUI to do this or your own host controller?

    Can you try reading back after writing the new configuration before issuing strat commnad?

    Thanks and Best Regards,

    Venkatadri S

  • Hi,

    I am used my own host controller. 

    I have read back to check the write command is OK. "But I read back the MOTOR_STARTUP1(84H) register, which the ALIGN_TIME=2(=100 ms);".

    More details: After power-on my controller (also to MCF8315C), I initialized all RAM registers, and then rotate motor, the align-time is also not my configured time.

  • Hi,

    They are one week passed, do you have any more feed-back?

    More details: After power-on my controller (also to MCF8315C), I initialized all RAM registers, and then rotate motor, the align-time is also not my configured time. The flow picture shows the phase current. And why the current is decreasing stepply from open-loop to closed-loop?

  • Hi,

    This is running MPET, can you check Speed KP, KI fields. Even any of this are zero when you give speed command device starts MPET whhc measures motor parameters to tune for speed loop. The current profiling is because MPET running. Can you share step by step how you are starting? Can you share the JSON file which you are trying.

    As I mentioned writing to EEPROM will not work if motor is in run state.

    I recommend use EVM and GUI , tune the motor and use the  tuned parameter to program from your host controller.

    Follow the instruction provided in the data sheet (6.6) about programing the RAM and register and writing to EEPROM

    Thanks and Best Regards,

    Venkatadri S

  • Hi,

    I didn't used the EEPROM, I directly write to RAM registers. Use the above register write example, I write new ALIGN_TIME value, and then control to rotate motor, the real align time is not change. But if I wait 150 ms (TBD) and then control to rotate motor, the real align time is updated. Do these meet your design? And how can i to eliminate the delay time?

    I want to calculate current from register value (phase A/B/C; id, iq), which the formula is: reg_value / 2^27 * base_current / 8. What's the value of base_current?

  • Hi ,

    Regarding update rate , we recommend any change to RAM registers do in IDLE state and wait for 200 ms and it takes effect.

    When motor is running update rate to RAM may vary based on Motor running priority.

    Base current value is 6.25A.

    Thanks and Best Regards,

    Venkatadri S

  • Hi,

    I have add a long delay (200ms) to wait for the write regs make effect.

    One more question:

    I read FG_SPEED_FDBK register (offset=196h) to calculate motor speed. When motor is move, the register value is varied. But when I stop or brake (hold) the motor, the register value is not a very low value (no speed), but it will keep with no change.  Why and how can I make the register value is low when motor is stop or brake?

  • Hi ,

    This register is Read only. You can also read the ALGORTHM_STATE value in parallel, this shows motor state, if IDLE or Brake.

    Thanks and Best Regards,

    Venkatadri S