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TMP121: & TMP123 - Continuous SPI Data Out when CS Asserted Low?

Tony Heglas
Prodigy 180 points
Part Number: TMP121
Other Parts Discussed in Thread: TMP123, TMP125

Hello, 

Got a fairly straightforward question regarding the TMP121/TMP123 and was looking to see if someone could help clarify something regarding the SPI output.  

What is the SPI SO pin output from these devices if the CS pin is continuously held low?  Will it continuously clock out the 16-bits containing the temp data from the most recent conversion (for example, the same as the TMP125) or will it only clock out the data once and then go into an idle/shutdown state until CS is released and re-asserted low? 

Thanks, 

  • 0
    TI__Expert 8890 points

    Hi Tony,

    Thank you for posting to the Sensing forum.

    Regarding the TMP121 and TMP123, if CS is pulled low any conversion in progress will terminate, and the device will be placed into shutdown mode. Temperature data from the last completed conversion prior to this is latched into the shift register and clocked out at SO on the falling SCK edge.

    Best regards,

    Nicole

  • 0 in reply to Nicole Khoury
    TI__Prodigy 180 points

    Nicole, 

    Thanks for the quick response.

    So to confirm, the most recent conversion data is latched into the shift register upon interruption via CS being asserted low and is clocked out on the falling SCK edge.  This is a one-time occurrence and the same data will not be re-loaded into the shift register to allow for continuous read by the host SPI device.

    In order to communicate another reading to the host device, the CS pin would need to be released, time allowed for another temperature conversion to occur, and then CS re-asserted low?

    Thanks!

  • +1 in reply to Tony Heglas
    TI__Expert 8890 points

    Hi Tony,

    Yes, that is correct. CS must be high for at least one conversion time (max 320ms).

    Best regards,

    Nicole