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TCA9548A: Verification of connection

Lixing Fu
Expert 3225 points
Part Number: TCA9548A
Other Parts Discussed in Thread: USB2ANY,

I have used TI USB2ANY for the I2C communication to configure the part to enable more connection. I consider the internal switches are FETs with low resistance. The I2C communication was finally successful, and I can read/write without issue (no NACK feedback). However, I used a multimeter to probe the two sides of the connection, for example between SDA and SD0. There is still high impedance connection. Is there any way to figure out if I have successfully connected SDA and SD0? I wrote 0x07 to the device, and I do not know if there is any problem with the communication. Thanks!

  • 0
    TI__Mastermind 23156 points
    Hello Lixing,
    I would look at it with a scope to verify the signal assuming that is being toggled. The USB2ANY schematics are available on our internal web site. The I2C lines connect directly to an MSP430. Do a search for USB2ANY in are Infolink sight and you will find it. It also includes the Altium project if you want to open it up and look at the layout or component information.
    -Francis Houde
  • 0 in reply to fhoude
    TI__Expert 3225 points

    Hi Francis, 

    Thank you very much for your reply. Yes I have looked into the schematic of USB2ANY. Actually I have other I2C devices on my board, and they have already got good communication, and takes correct action to my commands. This verifies the the I2C communication is good. However, looks like TCA9548A still does not work. Here are my specific questions:

    1. If one channel is turned on, will I be able to measure a low resistance between SDA and SDx ?

    2. I2C commands have receivved ACK, which means the communication is good. If there is no connection between SDA and SDx, what can be possible issue be?

    Thanks,

    Lixing

    fhoude said:
    Hello Lixing,
    I would look at it with a scope to verify the signal assuming that is being toggled. The USB2ANY schematics are available on our internal web site. The I2C lines connect directly to an MSP430. Do a search for USB2ANY in are Infolink sight and you will find it. It also includes the Altium project if you want to open it up and look at the layout or component information.
    -Francis Houde

  • 0 in reply to Lixing Fu
    TI__Guru 62920 points
    Hi Lixing,

    Sorry for the delay - Francis is out of the office on vacation currently.

    This device does not work exactly like a simple FET switch in which a low resistance path is enabled whenever a channel connection is configured. Instead, when a channel is active the "low" levels will pass through the switch (which will have a low series resistance) but the "high" levels will be blocked. This architecture is needed to support voltage level translation on either side of the switch by allowing the external pull-up resistors to set the logic "high" levels. If you are successfully communicating through the channel that you have enabled, then you know that the switch is working properly.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Expert 3225 points
    Thank you very much Max. That answers my question.