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Original question:

BQ78350-R1: BQ78350-R1

BQ78350-R1: Communication is happening normally even if the PEC is not send by the microcontroller

Shreyas Shroff1
Prodigy 180 points
Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350, BQSTUDIO

Hi Team,

In SMB configuration the HPE is 1 i.e PEC on host communication is enabled. The SpecificationInfo() is having the the value 0x31. 

I am communicating over SMbus by not writing or reading the PEC byte but, still teh communication is happening with bq78350.

I need to understand how the commmunication happens with bq78350 even if PEC is not sent by host MCU.

Regards,

Shreyas Shroff

  • 0
    TI__Guru* 81034 points

    Hi Shreyas,

    The BQ78350 will respond to the host with or without the PEC byte. If the PEC byte is sent and it is incorrect, it will respond with a NACK. For example, by default BQStudio sends the PEC byte and the BQ78350.

    The HPE bit is for BQ78350 broadcasts to the host - if this bit is enabled it will include a PEC byte in the broadcasts.

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt,

    Does it mean we can write to bq78350  even if PEC is not sent from micro-controller?. I am using NXP micro-controller.

  • 0 in reply to Shreyas Shroff1
    TI__Guru* 81034 points

    Hi Shreyas, 

    Yes, the BQ78350 can be written with or without PEC. However, if a PEC byte is sent, it will be validated by the BQ78350 before allowing the write. 

    Best regards,

    Matt

  • 0 in reply to Matt Sunna
    Prodigy 180 points

    Hi Matt,

    Thank you for the above inputs. 

    I am not facing issue while reading the PEC value from bq78350-r2 IC. The salve address to read the PEC is 0x17

    1. I am reading 0x1A specificationinfo() from bq78350-r2 and get 2 byte value as 0x31 and 0x10.

    2. If the value the value is 0x31 it support the PEC so, next time I am reading the data with PEC and I get 0x31 , 0x10 and 0xAA. 

    3. When I am calculating the PEC having CRC_KEY(C(x) = x8 + x2 + x1 + 1.) as 7, I get the value after performing CRC8 as 0x28

    I would like to know why bq78350-r2 is sending 0xAA as it PEC value. If this value is correct how it is calculating the PEC?.

    Regards,
    Shreyas Shroff

  • 0 in reply to Shreyas Shroff1
    Prodigy 180 points

    Hi Matt,

    Thank you for the above inputs. 

    I am facing issue while reading the PEC value from bq78350-r2 IC. The salve address to read the PEC is 0x17

    1. I am reading 0x1A specificationinfo() from bq78350-r2 and get 2 byte value as 0x31 and 0x10.

    2. If the value the value is 0x31 it support the PEC so, next time I am reading the data with PEC and I get 0x31 , 0x10 and 0xAA. 

    3. When I am calculating the PEC with CRC_KEY(C(x) = x8 + x2 + x1 + 1.) as 7 on slave address nd received data 0x17 0x31 and 0x10 I get the value after performing CRC8 as 0x28.

    I would like to know why bq78350-r2 is sending 0xAA as it PEC value. If this value is correct how it is calculating the PEC?.

    Regards,
    Shreyas Shroff

  • 0 in reply to Shreyas Shroff1
    TI__Guru* 81034 points

    Hi Shreyas,

    I think the example in this other thread might be helpful: https://e2e.ti.com/support/power-management/f/196/t/869904

    The PEC calculation needs to include the entire sequence: 0x16 0x1A 0x17 0x31 0x10

    I confirmed the 0xAA result using this online tool: https://crccalc.com/

    Best regards,

    Matt