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ADS131A04EVM: SPI Bus Monitoring using J3

MT_CA
Prodigy 50 points
Part Number: ADS131A04EVM
Other Parts Discussed in Thread: ADS131A04

I am trying to monitor the SPI bus using a Total Phase Beagle I2C/SPI bus monitor connected to J3 on the processor side of the EVM. The registers of the ADC read fine. The Beagle SW run fine and shows transactions. However, Scripts, from the Delta-Sigma ADC Evaluation Software, do not run. The UNLOCK command (1st in the script) causes the D1 LED to turn off and times out. 

Has anyone run the TI ADS131A04EVM SW and used J3 to monitor the SPI bus successfully?

  • 0
    TI__Guru 55312 points
    Hi MT,

    Thanks for your post and sorry for the delay in response! We'll take a look and get you an answer shortly.
  • 0 in reply to Alexander Smith
    TI__Guru 66406 points
    Hi MT,

    Can you share a screen capture of the Console tab after you start the software and run the script?

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    Here are the registers before the script and the script tab after the script is run.

    the script hangs after the UNLOCK command and D1 turns off

  • 0 in reply to MT_CA
    TI__Guru 66406 points
    Hi MT,

    Thanks for sharing that. It seems clear that the GUI is stuck since it is not receiving an acknowledgement from the microcontroller on the EVM. Are you simply monitoring the SPI bus, or are you trying to control the ADS131A04 with an external microcontroller?

    Are all jumpers/switches still in their default position according to page 4 of the User Guide?

    Can you please disconnect the bus monitor, disconnect/reconnect the EVM USB cable, and then restart the GUI and run the 'Basic startup' script?

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    Hi,

    I am just trying to monitor the SPI bus. I'm not trying to control it (yet).

    all jumpers are in the default positions.

    i can disconnect (or press the the 'reset' buttons for the microprocessor and ADC) and run the basic script.

    Everything works fine if nothing is connected to J3.

    J3 Pin 7 (CS) is especially sensitive, any connection (scope, bus monitor) will cause the EVM to hang

    Thanks for your help

  • 0 in reply to MT_CA
    TI__Guru 66406 points
    Hi MT,

    Thanks for the confirmation.

    It is troubling to hear that the SPI lines are that sensitive - we do want our customers to have the ability to monitor the SPI transactions and learn how it works. I can't say that any logic analyzer I've used has caused this type of issue.

    Can you verify on a scope that /CS is being toggled? If it cannot reach the logic 0 level, then the SPI frames will not be decoded correctly.

    Best Regards,
  • 0 in reply to Ryan Andrews
    Prodigy 50 points
    Hi Ryan,
    I cannot monitor the CS line with a scope. The EVM does not like that. D2 or D1 goes OFF and a reset of either the processor or the ADC causes D1 and D2 to go OFF and D3 to turn RED.
    However, the Total Phase Beagle SPI Monitor does function before running a script indicating the CS line is toggling because it shows 'transactions' that do not show if the CS line is not connected to it.
  • 0 in reply to MT_CA
    TI__Guru 66406 points

    Hi MT,

    I'm sorry, but I'm unable to reproduce your issue. I can reliably probe the /CS signal on J3 with a scope immediately after power-up and while running the 'Basic Startup' script without any issue.

    Best Regards,

  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    HI Ryan,

    I changed my probe setting to x10 and it does not disrupt the SPI signals.

    The x10 probe specification is; 200MHz, 10MΩ, 16pF. The x1 probe specification is; 6MHz, 1MΩ, 95pF. The x1 Probe does corrupt the SPI signals.

    We found this on the Total Phase website; "The input characteristics of the Beagle I2C/SPI Protocol Analyzer are approximately 15pF parasitic capacitance and 10uA leakage current, which calculates to a minimum of 330k ohms. In actual practice, it is more like 1M ohms" 

    The Beagle I2C/SPI Protocol Analyzer is similar to the x1 probe and seems to be incompatible with EVM module.

  • 0 in reply to MT_CA
    TI__Guru 66406 points
    Hi MT,

    Thank you for the update. This is really helpful to know for future reference.