This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADS7128: RMS conversion doesn't start

Part Number: ADS7128

How is the rms conversion supposed to work.

Starting from reset, here is what I have done

writing 0x20 to OPMODE (autonomous mode)

Then I write the channel Id to RMS_CFG

Then I write 0x80 to GENERAL Config register.

Then I poll System Status, and nothing ever happens.

What am I missing.

  • Hello Jean,

    My first suggestion is to use the device is manual mode this will help to easy see what the device is doing. 

    Below are the steps needed to complete an RMS conversion:
    1. Select the channel for the RMS computation using the RMS_CHID field in the RMS_CFG register.
    2. Define the time over which the RMS is to be computed by configuring the RMS_SAMPLES field.
    3. Start the RMS computation by setting RMS_EN to 1 in the GENERAL_CFG register.
    4. The device starts computing the RMS result when the sample size defined by RMS_SAMPLES is converted
    on the analog input selected for RMS computation. An additional 40 samples must be converted to complete
    the RMS computation. I believe this is what is likely missing.

    In manual mode, you will need to trigger these. In autonomous mode, based on what you shared, you have not set the channel in register AUTO_SEQ_CH_SEL Register (Address = 0x12), thus the device is not sampling any channels.