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TMS320F280039C: RPT_START Periodic reset when SCL pull low before send ACK signal?

Shaoxing Ke
Expert 3590 points

Part Number: TMS320F280039C

Hi Experts,

I am asking for my customer.

After the PMBUS host reads the address and before giving ACK, the PMBUS slave pulls SCL low. At this time, the code reads the PMBSTS register and finds that RPT_START will be set continuously. CH3 in the figure below is the test signal. The PMBSTS register is read once every 50us. When RPT_START is set, GPIO torggle. So PMBUS master can not work normally with PMBUS slave, Could you give us any suggestion/Dir? Thanks.

Purple is RPT_START//50 us GPIO Torggle, Bule is SCL signal.

  • 0
    TI__Mastermind 20435 points

    Hi Shaoxing,

    Are you using automatic or manual ACK? Are you using any of the message commands? I'm referring to configuration and commands found in this section. It looks like once there is a repeated start and the target address, the module provides a data ready and request interrupt when using messages like the read byte and read word.

    If the clock is being held low, the module is stalling the bus until an ACK can be received (known as clock stretching). Knowing the above two things, seems that the module isn't ready for next data transmission. The PMBSTS has bits to check out for clock high / low timeouts. 

    Aishwarya

  • 0
    TI__Mastermind 20435 points

    Shaoxing,

    Have you been able to resolve this issue? If there are no more questions, I will go ahead and close this thread  

    Best Regards,

    Aishwarya