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TMP461EVM: Negative Temperatures extended format

Mark Philip Felipe
Genius 10820 points
Part Number: TMP461EVM
Other Parts Discussed in Thread: TMP461

Hi Team, assisting a customer that needs clarification.

How the TMP-461 represents negative temperatures in the Extended Format using both the High Byte and Low Byte.  Do we always add the fractional temperature (Low Byte) as a positive number to the High Byte value?  For example, if the temperature is -15.0625 deg C, the High Byte Extended (-16) would get added to the Low Byte (0.9375) and the 12 bit Extended Format representation would be 00110000 1111 (High Byte, Low Byte).  Another example is -0.4375 deg C. The High Byte Extended (-1) would be added to the Low Byte (0.5625) and the Extended Format representation would be 00111111 1001 (High Byte, Low Byte).  Is this correct? 

Thank you

-Mark

  • 0
    TI__Mastermind 28070 points

    Hi Mark,

    Thank you for your question. You are correct. 

    In extended mode for the TMP461, the high and low byte were intended to be concatenated and interpreted as a single unsigned 12-bit value, converted to C, and then have 64C subtracted from the result. As you've noticed, you can also find this by adding the low byte value to the high byte after its already been offset. 

    Using the order I suggested for -0.4375C, you would have a register value of 0x3F90. Prior to offset you would see this as a value of 63.5625C, which you could then just subtract 64 from to get -0.4375C. Like you've done though, you can also apply the offset first, and interpret it as a high byte of -1C, and a low byte of 0.5625C

    Best Regards,
    Brandon Fisher