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PCA9545A: Enable all port in same time

user4979899
Expert 3080 points
Part Number: PCA9545A

Hi Sir,

just double confirm with you that if set B0/B1/B2/B3 =1, then all channels will be enable at the same time, correct?

  • 0
    TI__Guru 62920 points

    Hi Anne,

    Yes, you are correct.  This would enable all channels.  Note that when enabling multiple channels their respective capacitive loading and pull-up resistances will combine effectively in parallel, so you would want to make sure that all the nodes can continue to support communication during this condition.

    Regards,
    Max

  • 0 in reply to Miguel Robertson
    TI__Expert 3080 points

    Hi Max,

    Thanks for your feedback.

    If PCA9545A can be placed between two SMBus Masters and Mater A control channel selection

    Once channel 0 enable, then Master B can communicate with Master A. is this allowable?

     

  • 0 in reply to user4979899
    TI__Guru 62920 points

    Hi Anne,

    From just the standpoint of the physical signaling the switch will work whether the high/low levels are coming from a master or slave.

    From a higher-level protocol standpoint, though, the master devices would need to be designed with this usage in mind.  This means that they would need to know when the bus is busy and not initiate communication until the bus goes idle (e.g., by detecting a stop condition).  And, if both masters start communication at the same time they would need to follow some arbitration logic to realize when a collision occurs and cease transmission if needed.  Many simple master devices cannot support this and would require an external device for multi-master arbitration.  The PCA9545A device would not be able to perform this function.  (There is currently not a TI device for this.)

    Regards,
    Max