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PCA9545A: PCA9545APW - I2C Switch

John Miller86
Prodigy 100 points
Part Number: PCA9545A
Other Parts Discussed in Thread: TCA9545A

Section 4 of the PCA9545APW  datasheet has a picture showing multiple slaves connected off of the downstream interfaces SD/SC[3:0]. But it is not clear how these downstream slaves are accessed. I understand that setting up the control register "enables" a channel but how does one access slaves of different addresses connected to the channels. For example, I have two slaves on SD0/SC0 and each has a different address. Does my I2C Master use their addresses - in other words, does the switch become transparent after writes to the control register enables SD0/SC0 ?

  • 0
    Guru 317370 points

    Yes. This device is a passive switch; all enabled channels are directly (electrically) connected to SDA/SCL, and all pull-up resistors work in parallel.

  • 0
    TI__Mastermind 26826 points

    John,

    Clemens is correct. Once a channel is connected, it becomes part of the I2C bus. Your microcontroller is able to speak directly with these downstream devices via the I2C bus once the PCA9545A has connected the channel to the bus via the appropriate command.

    I'd highly recommend looking at the TCA9545A, which is a pin-for-pin upgrade to the PCA version of the device. It uses newer technology to improve performance, and you will notice significantly better pricing for the device. It is offered in the TSSOP package that you are currently using.

    Best,

    Danny