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No output on a TCA9548A

Conor Gray
Prodigy 60 points
Other Parts Discussed in Thread: TCA9548A, TCA9545A, LDC1614

Hi,

I am using a TCA9548A (on a DFR0576 Gravity board).

I can write to and read from the control register without any issues (the read data reflects the write data, so I know it is been written correctly).

I also checked in on a scope and the waveforms look correct.

The master I am using is a National Instruments NI-8452 (I have disabled the pullups on it as the DFR0576 board has pullups to 3V3 on both the input channel and all the 8 output channels).

However when I enable any of the output channels I don't see anything appear on the output.

I have disconnected the I2C devices from the TCA9548A outputs but still don't see any activity on the output lines.  They remain at 3V3.

I had also tried the TCA9545A (4 channel part) earlier with the exact same symptoms.

I am baffled as to what is the cause.  Any help, suggestions would be greatly appreciated.

Kind regards,

Conor.

  • 0
    Prodigy 60 points

    Also I have tried a hardware reset of the device (after which I re write the control resister to enable an output channel) and still no activity on output SCx or SCx, they just reamin at 3V3

  • 0 in reply to Conor Gray
    TI__Guru 58710 points

    Hi Conor,

    Our I2C switch devices require a stop condition to be issued by the I2C controller after a direct write to it. Doing reads after a write without a stop condition (using a restart condition) will not allow our device to execute the previous write command. 

    Can you verify the stop condition occurs after the write?

    If you are still having issues after confirming, please share the schematic of our device and a scopeshot of the I2C write command so we can try to find the root cause.

    -Bobby

  • 0 in reply to BOBBY
    Prodigy 60 points

    Hi Bobby,

    Thanks so much, that did the trick!

    I was using a Labview instruction that did a combined Write followed by Read, that did not issue the Stop Condition until the Read was complete.

    When I separated out the Write and Read, it started working straight away.

    I had used this National Instruments NI-8452 with other TI devices including the LDC1614 without any issues, so I had not suspected the I2C sequence.

    Thanks again,

    Kind regards,

    Conor.