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TMP125: Chip Select

Mark Ackerson
Genius 10190 points
Part Number: TMP125

For the TMP125, if we hold SI (DIN) to GND to keep the part in continuous mode, is there any issue if CS is held low for more than 16 clocks?  If CS was GNDed, does the part start new conversions?  Or does CS need to be toggled?

Regards,
Mark

  • 0
    TI__Mastermind 28070 points

    Hi Mark,

    I've tested this on a quick setup and it does appear to work. It doesn't look like CS needs to be toggled to update the data. I was able to get fresh temperature reads with CS grounded, and average current draw was roughly the same as when CS was toggled.

    My only concern would be that you could run into a case where you are attempting to read the temperature at the same time that the TMP125 is trying to update the internal temperature register. I haven't been able to generate any of those conditions in my setup, so it may be fairly rare, but in theory it could lead to seeing some erroneous data points. 

    Please let me know if you have any follow-up questions. 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    TI__Genius 10190 points

    Hi Brandon,

    Thanks for the response.  Due to pin resources, The customers is planing to share the TMP125’s CS with another SPI device (the SOUTs of each spi slave device are fed into different inputs and don’t share the same net).  

     If CS is shared, are there any issue/concerns if the TMP125 is sent a non multiple of 16 SCLKs while CS is asserted low? The TMP125’s data would be read out during the first 16 SCLKs.

    Thanks,
    Mark

  • 0 in reply to Mark Ackerson
    TI__Mastermind 28070 points

    Hi Mark,

    Here's a LA Capture of the TMP125 responding to a three byte read. It looks like the TMP125 will continue to return data, but that data will be a repeat read of the temperature register on the device. So if you clock out three bytes you will see the MSB again, if you clock out 4 bytes you will see the same read twice. They would just need to ignore the extra data to make this work. 

    The next time they request data the device will still return the MSB first, even if you received it in a previous read.

    Best Regards,
    Brandon Fisher