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ADS7924: Retrieving data without stopping

Gilad Furst
Prodigy 50 points
Part Number: ADS7924

Hello.

I'm designing a system with ADS7924. It has a dual role: it will (1) provide the samples to the Host for a closed-loop control, and (2) generate an alarm if the levels exceed the threshold.

The Alarm acts as a fail-safe and (using additional devices) disconnects the monitored system even if the Host is stuck for some reason.

For this reason I need to be able to monitor the sampled values _without_ stopping the automatic conversion.

This is in contradiction to the datasheet which states: "TI _suggests_ interrupting this mode and stopping the automatic conversions, either by setting the mode to Idle or configuring the alarm to do so, before retrieving data."

What would happen if I don't stop? will the values be wrong? will the alarm malfunction? is there any design which will lessen such issues?

Additional information: it will be possible to clean-up the data in the Host somehow if need be. Power savings is not an issue. I intend to use Auto-Scan Mode, but Auto-Scan With Sleep Mode or Auto-Burst Scan With Sleep Mode can also be used if this improves matters.

  • 0
    TI__Mastermind 24970 points

    Apologies for the late response, we are looking at query and will respond soon
    Regards, Cynthia

  • 0 in reply to Cynthia
    TI__Mastermind 24970 points

    Hello,

    It is suggested to stop the automatic conversions because the register contents are updated based on when the channel is sampled, not when the register is read. This means that if you try reading a register content and a conversion occurs, the data could become corrupt.

    Having the host locked up brings in the dillema.

    Have you looked at the ADS7142 ? It has an Autonomous Mode with Post Alert Data; after an alert has been triggered, the device will store up to 16 entries after the alarm in a data buffer, the host can access the data once it is able to. Note the device does have tradeoffs from the ADS7924 functionality. When in Autonomous mode you will not be able to read the data out, not until a triggering event, the device in manual mode can provide data out for each conversion.

    Regards, Cynthia