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PCA9545A: Default I2C address

Art Mecina
Genius 16655 points
Part Number: PCA9545A

Hello Guys,

Good day.

Customer are using the PCA9545A in a project to connect several I2C device to a Particle Boron and wants to know the following.

1.) What is the default I2C address for the PCA9545A? customer scanned and received 0x70... is this correct?

2.) They are connecting ADXL345 Accelerometer and a VL53L1X ToF sensor to the PCA9545A. Should be be able to scan their I2C addresses as well, or shall they only pick up the address of the PCA9545A?

They have the Particle Boron connected to the PCA9545A and have the ADXL345 installed. When scanning they only pick up the 0x70 address and would like to know if this is to be expected. They are using custom PCB's and need to make sure everything is working correctly.

Thanks in advance!

Art

  • 0
    TI__Guru 53555 points

    Hi Art,

    These results sounds like expected behavior for the system you've described. 

    1. The address of PCA9545A will depend on the state of the A1, and A2 pins. When both pins are tied to ground, the resulting address will be 0x70.

    2. When PCA9545A first powers-on, all of the downstream switches will be disabled. This means that any device connected to the busses on channels 0 through 3 will not be available to a Master on the main bus. To access these downstream devices, their respective channel will need to be enabled on PCA9545A by writing to the corresponding bit in the device's control register (see Section 9.6.2 on the datasheet). This will enable the channel by effectively connecting it to the main bus, allowing the Master to communicate with any device on this channel. 

    I hope this information is helpful. Let me know if you have any other questions.

    Regards,
    Eric Schott

  • 0
    Guru 316940 points

    1. The PCA9545A does not have a "default" address. The address is chosen by the A0/A1 pins; if both are connected to GND, then the address you have chosen indeed is 0x70.

    2. An address scan (or any other I²C access) will reach the devices only if they are on one of the currently enabled channels. After a reset, all four channels are disabled by default.