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TCA9535：Device cannot be found

user4205571
Expert 1390 points
Other Parts Discussed in Thread: AM5708, TCA9539

HI：

Custom AM5708 board card

SDK：5.3

Hardware schematic:

The application layer sets the reset signal

# RESET gpio4_29
echo 125 > /sys/class/gpio/export
echo "out" > /sys/class/gpio/gpio125/direction
echo 1 > /sys/class/gpio/gpio125/value
sleep 1
echo 0 > /sys/class/gpio/gpio125/value

The device could not be identified using the i2cdetect command

What should we pay special attention to about the TCA9539 chip?I can't identify the device.

  • 0
    TI__Guru* 77461 points

    Hey User,

    I am unfamilar with the i2cdetect command but can confirm how it does it's detection? Does it perform a read transaction from the I2C slave?

    If so, this may be why you are not detecting the TCA9539. The TCA9539 requires a write before a read otherwise it will NACK. Our i2c IO expanders require you address a pointer before it will ACK to a read transaction.

    My suggestion: try to confirm the device is present with a write transaction instead.

    If you are still having problems, let me know and try to grab some o-scope waveforms of SDA/SCL when our device NACKs its address.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Expert 1390 points

    HI：

    Does it matter if I don't set the interrupt signal（INT pin）？

  • 0 in reply to BOBBY
    Expert 1390 points

    Hi：

    I feel like after I reset, the chip doesn't recognize.I can't find the device. I2c write will fail.

    I do i2c reads and writes in the application layer.

  • 0 in reply to user4205571
    TI__Guru* 77461 points

    Hello,

    "Does it matter if I don't set the interrupt signal（INT pin）？"
    The INT pin is an output and not used for I2C communication so this does not matter.

    "I feel like after I reset, the chip doesn't recognize.I can't find the device. I2c write will fail."

    Can you provide scope shots of the SDA/SCL lines when you try to write to the device after a reset?

    -Bobby

  • 0 in reply to BOBBY
    Expert 1390 points

    Hi：

    1、SDL signal

    2、SCL signal

    3、Interrupt singnal

    4、reset singal

  • 0 in reply to user4205571
    TI__Guru* 77461 points

    Hello,

    It looks like your reset signal is GND which would make it so the device is held in reset. Our device would NACK all communication in this mode and you would not be able to communicate with it.

    Please make the reset signal HIGH.

    Also, you should place 2 o-scope probes on SDA and SCL then trigger on the falling clock edge in NORMAL mode in order to capture I2C communication. If you are in auto Mode on the o-scope (like in your image) all we will see is the idle I2C bus.

    Thanks,

    -Bobby