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bq20z655-R1 BCAST bit dependency with new SBS 1.1 Master Mode Bus Start Collisiton Update feature

Kenneth Habegger
Prodigy 60 points
Other Parts Discussed in Thread: BQ20Z655-R1

In the bq20Z655-R1 release we have noted a preemption of the broadcast capability with the BCAST bit set (Operation Cfg B, Low Byte, Bit 0 = 1) when the SBS 1.1 Master Mode Bus Start Collisiton Update feature is enabled (default settings).   The default setting for SMB Sync Command is 0xff (any command) with an SMB Sync Delay of 50 (50 X 488uS = 24.4mS).   The intent of this feature is to delay the mastering of the SM bus by the gas gauge after it has received an SMB command to reduce the likelihood of collisions.   However, unless the feature is deactivated (SMB Sync Delay = 0), we have observed that no periodic (~50 sec) broadcast messages for ChargingVoltage() and ChargingCurrent() occur when the SMB signals are pulled up by a charger or host, and alarm messages appear to be inhibited as well.    Have others observed this behavior?   Solutions?

  • 0
    TI__Expert 7330 points

    Hello,

    I have confirmed with Dallas that setting SMB Sync Delay = 0 will provide desired broadcast behavior.

    Best regards, Keith

  • 0 in reply to Keith Keller
    Prodigy 60 points

    The Application Report SLUA623--October 2011 entitled the bq20Z655 to bq20Z655-R1 Change Document states in section 3  SBS 1.1 Master Mode Bus Start Collision Update , "... However, to support improved robust communication conditions when the bq20z655-R1 is enabled to broadcast, it has been enabled with additional SMBus control. The bq20z655-R1 ensures a delay between receipt of a transaction and mastering the bus."   Our findings seem to indicate that when the Master Mode Bus Start Collision Update feature is enabled it does not provide "additional SM bus control", but a loss of SM bus broadcast operation.  The entire intent of the feature is to delay a broadcast event, not disable it.  This feature is only valid when BCAST = 1 and yet it appears to preempt broadcast.