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How Do I Troubleshoot My Setup when the I2C SDA Line is Held Low?
Rena Ayeras

Bits of data that are blocked when I2C SDA line is held low.

Illustration by Geralt

Question from the Customer:

I am using the Aardvark I2C/SPI Host Adapter to send commands to a temperature sensor controller on the SMBus. However, after connecting the Aardvark adapter, the SDA line is held low – no data transactions. What can I do to release the SDA line?

Response from Technical Support:

Thank you for your question! The problem that you described could be a configuration issue. We recommend verifying the Aardvark adapter works correctly. If testing verifies the Aardvark adapter is functional, we recommend analyzing the configurations you are using with your setup.

We have two recommendations for running tests, which are described below.

Basic Troubleshooting with One Aardvark Adapter

This method verifies basic I/O functionalities with Control Center Serial Software and a digital multi-meter.

  1. Remove the Aardvark adapter from your target system.
  2. Connect the Aardvark adapter to your computer.
  3. Open the Control Center Serial Software, connect to the Aardvark adapter, and choose the GPIO only mode.
  4. Disable the I2C pull-ups in the Aardvark menu.
  5. Test writing output signals:

    1. Set all the signal directions to OUT and set all the signals to digital 0.
    2. With the digital multi-meter, verify that output level of each GPIO pin is 0V.
    3. Set all the output signals to digital 1.
    4. With the digital multi-meter, verify the output level of each GPIO pin is 3.3V.
  6. Test reading input signals, which is similar to the previous test.

    1. Send the voltage levels of 3.3V or 0V to each input pin: digital 1 and digital 0.
    2. With the Control Center Serial Software, see if the Aardvark adapter is reading the signals correctly.

Advanced Troubleshooting with Two Aardvark Adapters

This test verifies more functionalities by using two Aardvark adapters. One adapter is in master mode, and the other adapter is in slave mode. Following is a summary of the procedure:

  1. Install two instances of Control Center Serial Software, and connect the Aardvark adapters to separate USB ports of the computer.
  2. Connect each Aardvark adapter to a separate instance of Control Center Serial Software.
  3. Configure one Aardvark adapter as the slave (target), and the other Aardvark adapter as the master.
  4. Have the master device send data to the slave adapter to read.
  5. Have the slave device send back the data to the master adapter, and verify the data read is correct.

For details, go to Two Aardvark adapters Tests with Control Center Serial I2C/SPI on Windows. The instructions have the Aardvark adapters configured for SPI. You can modify the steps for I2C operations.

We hope this answers your questions. Additional resources that you may find helpful include the following:

If you want more information, feel free to contact us with your questions, or request a demo that applies to your application