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bq78350, reading wrong values

Yoav Gross
Intellectual 365 points
Other Parts Discussed in Thread: BQ78350

Hi,

I am getting some false readings from the bq78350, 

I have enabled pec to avoid just that, however, sometimes when I request pack voltage (SBS CMD 0x09), I get 3600 . this is the answer of SBS CMD 0x19 - DesignVoltage().

I tried sending a request with a wrong pec - and got an answer from the bq78350. 

Is there a way to enable pec on both directions? bq78350 -> host and host -> bq78350?

  • 0
    Intellectual 365 points
    This is a little confusing,
    I added the wrong PEC at the write SBS CMD, but tested it at the read SBS CMD...
    I actually dont have PEC when I send the SBS CMD in the read function.. should I just add PEC there?
  • 0 in reply to Yoav Gross
    Mastermind 8415 points
    Hi Yoav,

    How are you sending the commands? From BQ Studio or some stand-alone application?

    Also, if you are using BQ Studio, make sure that the Automatic refresh is disabled. If BQ Studio is trying to refresh its values while you attempt to read some values, you will most likely get some garbage values.

    If you are using a stand-alone application, check what is going on with a logic analyzer by tapping yourself onto the SMBD and SMBC lines.

    And before you use a logic analyzer, just check your signal with an oscilloscope to make sure that the voltages are good and that the integrity of your signal is not compromised by noise or something else.

    Michel
  • 0 in reply to Michel Solecki
    Intellectual 365 points
    Hi Michael,

    Thanks for responding.
    I will do just what you suggest to learn why the values are sometimes wrong.

    but I do want to know if there is support in pec in SMBus Read Word, when sending the SBS command to the bq78350. my problem is getting a validated answer on the incorrect question.
  • 0 in reply to Yoav Gross
    TI__Guru 73830 points

    Michel

    The gauge should support PEC for read. Do you have PEC enabled? Also, here is some general information on our SMBus communications protocol.

    Tom

    6012.SMBus made simple_v6.pdf

  • 0 in reply to ThomasCosby
    Intellectual 365 points
    Tom,

    it was my question not Michael's.

    The PEC in "SMBus Read Word (with PEC)" is only on the answer.
    My problem is I am trying to read 0x09, but ,sometimes, getting an answer on 0x19.
    There is no PEC on the "SBS CMD" I am requesting in the SMBUS Read Word.
  • 0 in reply to Yoav Gross
    Mastermind 8415 points
    I haven't worked on the BQ78350 in a while, but after reading the TRM, it should support PEC even for read word. And from what I recall, the PEC is only going to be in the response that you get, not on the first write (your command).

    I hope someone from TI can confirm this.
  • 0 in reply to Yoav Gross
    Mastermind 8415 points
    I'll let Tom take over from here, since it might be some hardware issue.
    But it seems illogical to receive a 0x19 response if you requested a 0x09. Check your signals to make sure that this is indeed what is happening on the line.