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ADS1115: Address 0x4B not found

Santiago Sierra Rios
Prodigy 20 points
Part Number: ADS1115

Tool/software:

Hello,

I am using an ESP32 along with 4 ADS1115 modules. I have successfully obtained the I2C addresses 0x48, 0x49, and 0x4A, and I can correctly read the analog channels from each of them. However, I am unable to find the 0x4B address, which according to the datasheet should be obtained by connecting the ADDR pin to the SCL pin.

What could I be doing wrong? I have tried multiple ADS1115 modules, but in all cases, I cannot detect the 0x4B address.

Any help would be greatly appreciated.

Thank you!

  • 0
    TI__Expert 7060 points

    Hi Santiago,

    Can you please share a capture of the I2C communication waveforms using a logic analyzer or an oscilloscope?

    The first I2C frame should look something like this:

    Do you get a NACK on the last bit of the frame when you try using the 1001011b address (ADDR pin connected to SCL)?

    It is possible you've constructed the address read/write incorrectly. The I2C address is 4Bh, but that is the upper 7 bits of the write. In your address, you use 4Bh as the byte and then and OR it with 0 or 1 for a write or a read. For the I2C address, you should 96h and then OR it with 0 or the 1 for the write or read. This is essentially shifting every bit to the left once to account for the read/write bit (8th bit of the frame). 

    Again, the best way to know what is going on is to see the digital communication with a scope to see what is going on.

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 20 points

    Hello,

    My problem is that when scanning the I2C addresses, the only one I can't find is 0x4B. I can find the 0x48, 0x49, and 0x4A addresses, and I can correctly measure signals with them. Now, do I need to make another configuration with resistors to find this address?

    I tried writing to the 4B address as you suggested (75 in decimal), but the device doesn't respond. According to what I obtained from the logic analyzer, the address is correctly constructed.

    I've used 3 different ADS1115 modules, and I get the same results with all of them. All the devices are new.

  • 0 in reply to Santiago Sierra Rios
    TI__Expert 7060 points

    Hi Santiago,

    You are right the address is correctly constructed.

    What is your SCL frequency?

    Can you share a schematic of your setup? This will help confirm if all the connections to the device are correct.

    Best Regards,

    Angel

  • 0 in reply to Angel Rodriguez de San Miguel Bermudez
    Prodigy 20 points

    Hi Angel
    The SCL frequency is 400kHz.

    These are my schematics

  • 0 in reply to Santiago Sierra Rios
    TI__Expert 7060 points

    Hi Santiago,

    The connections seem correct, and the address is correctly constructed, so I'm not sure what the issue could be. 

    Something you could try is using a lower SCL frequency and see if you see any difference, since 400kHz is the upper limit before having to use high-speed mode. 

    It seems like the clock cycle for the Acknowledge bit is always a little longer. Why is that? This shouldn't be a major issue for communicating with the device, but I wonder why that is the case and if this has something to do with having trouble using the SCL address. 

    It is also possible that the devices were damaged at some point, or even be counterfeit. 

    Best Regards,

    Angel