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Original question:

ADS9234R: Question for SPI communication

ADS9234R: SPI configuration with shared nCS and CONVST

Alexander Drexel
Prodigy 10 points
Part Number: ADS9234R

Hi,

I have a question about the pin configuration where nCS is tied to CONVST as shown in Figure 67 on p. 40 of the datasheet.
How is the device configuration handled in this case because it's not possible to keep CONVST high during register write or read?
There is a note in the datasheet (7.6.3) that the host must keep CONVST high for reading and writing the registers. This is not possible due to the connection to nCS.

How should the SPI communication look like in this case?

Best regards,
Alex

  • 0
    TI__Guru 60606 points

    Hi Alex,

    Thank you for your post.

    I believe the intention of showing this minimal device configuration is for customers who do not need to configure the device registers and can use them in their default setting. You are correct that in order to read/write registers, you must be able to control /CS independently of CONVST.

    Best regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 10 points

    Hi Ryan,
    thanks for your answer.

    When I was looking into the timing diagrams, a CONVST falling edge should not trigger something in the ADC.
    If /CS and CONVST are set low at the beginning of the frame, the register write will be performed but at the end of frame when /CS and CONVST change from low -> high the ADC would start a new conversion.

    Will the register value be written properly in this case?
    Is it possible to only write registers using this minimal configuration?

    Br,
    Alex

  • 0 in reply to Alexander Drexel
    TI__Mastermind 23050 points

    Hey Alex,

    Ryan is out of office at the moment so I will try to assist. I'm actually not certain whether or not the device would be able to receive a write correctly and update the configuration with the pins tied together. In any case though I would not recommend doing this as you would have no way to verify what the actual state of the converter is, whether writes went through as intended, or do things like CRC checks. The case where these pins are tied together is provided as an option for customers that intend to use the device in the default configuration and don't need to do any programming. 

    Best,

    Zak

  • 0 in reply to Zak Kaye
    TI__Mastermind 23050 points

    Hi Alex,

    Just wanted to let you know that we are double checking this functionality with the design team!

    Best,

    Zak

  • 0 in reply to Zak Kaye
    Prodigy 10 points

    Hi Zak,
    thanks for clarifying it again within your team.
    It sounds reasonable to me to always check the register values if the ADC is configured different to the default setting.
    It would be nice if the ADS9234R datasheet could be updated, to make it clear that with the minimum pin configuration registers couldn't be written via SDI.

    This is a proposal how it could be better visualized. Screenshot taken from SBAS876C –AUGUST 2018–REVISED JUNE 2019


    Br,
    Alex