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ADS7956: Auto Mode1 communication error

Part Number: ADS7956


I am sorry that my reply was delayed in the previous post.
I share the customer situation.

>The Auto mode 1 will sampled channels that have been pre-programmed. If no channels were selected then this mode will not function properly.
>Can you provide more information about the issue? does the device previously work in mode 1, displaying the correctly pre programmed channels
>Then, without anything changing, it stops to scan and only shows channel 0?
The phenomenon occurs while the DC motor is operating. Therefore, the setting is not changed before and after the phenomenon.

>Is the customer changing from different modes and mode 1 does not work when called on?
Switching to another mode is difficult because it involves software changes by the customer.
However, it will be restored by sending the Auto Mode 1 command again.

>Does the customer have noise on the digital communications that could disrupt expected communications?
Due to the configuration of the equipment, the measurement is performed with the jumper wire pulled out, so it is an environment where it is easy to receive external noise.

Based on these, let me ask a new question.
What are the conditions under which the settings are reset (returned at power-on)?
Is there anything else that causes the ADC settings to revert to their initial state other than restarting the power supply?

Best regards,
Yuto Sakai

  • Yuto,

    I will support this question as Cynthia is out for a few days.  I will review your post and get back soon.

  • Yuto,

    1.  If I understand correctly: the system works correctly until the motor is turned on.  Once the motor is turned on, the device becomes locked into Auto 1 mode.  Is this correct?

    2.  If I understand correctly: Jumper wires with the digital signals are pulled out of the system making it susceptible to noise.  Correct?

    3.  Can you measure the digital signals during the noise event?  I bereave that you will see significant digital errors from noise coupling in.  Noise glitches can be interpreted as a clock or data signal and this can put the device internal state machine into a bad state.  This is very likely your issue.  Now we just need to see if we can find a way to shield your circuit from the noise. 

    4.  Can you replace the jumper wires with shielded wires?  Is the "jumper wires pulled out" for debug purposes.  If it is just a few wires a shielded coax cable with the shield grounded on one end is a good approach to minimizing the coupling of the digital signal.

    5.  Depending on the noise level, a 50 ohm resistor in series with the digital lines may help with the noise.  The 50 ohm resistor forms a filter with the parasitic digital i/o line to minimize the impact of noise spikes. 

  • Hi Art-san,

    Thank you for your reply.

    1 is a little different.
    After setting Auto Mode 1 and turning on the motor, the phenomenon that only 0ch is acquired occurs after a while.
    About 2 is correct.
    Thank you for your detailed explanation of noise countermeasures.

    Considering phenomenon 1, it seems that the settings have been reset.
    What are the possible causes for the settings being reset?
    Is it on the data sheet?

    Best regards,
    Yuto Sakai

  • Yuto,

    The data sheet assumes that you will follow the device timing requirements.  A noise event can be interpreted by the device to be an extra clock.  This extra clock will violate the timing requirements and can potentially put the device's internal state machine into a bad state.  The data sheet cannot account for cases where timing specifications are violated, because depending on the violation, the behavior can be different.  I hope the noise counter measures help you resolve the issue.  Let me know if you have further questions.