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TMP75 question.

Anatoly Odler
Expert 1870 points
Other Parts Discussed in Thread: TMP75

Hi,

We are using the TMP75 in our embedded system.

I need to configure it via DSP SW through the I2C protocol commands.

Do I need to perform the General Call with 0x06 command on device initialization or is it enough to perform the 0x04 command with the General Call?

Anatoly.

  • 0
    TI__Mastermind 27715 points

    Hello Anatoly,

    Using the 0x06 command in the second byte will cause the TMP75 to latch the status of its address pins and reset its register values, while the 0x04 command will cause the TMP75 to only latch the status of its address pins. Which command you decide to use is dependent on whether or not you want the TMP75 to reset prior to initialization.

    I would recommend using the 0x06 command and performing a full reset prior to configuration.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Expert 1870 points

    What do you exactly mean saying "report its address"?

  • 0 in reply to Anatoly Odler
    Expert 1870 points

    I have more questions.

    • Does the shutdown mode affects ALERT pin somehow? 
    • Does the temperature register represent the value in two's compliment form with the first most significant bit as a sign bit?
    • Does the four LSB's of the temperature value represent the fraction fraction value?
    Thank you.
  • 0 in reply to Anatoly Odler
    TI__Mastermind 27715 points

    Anatoly,

    The official spec from NXP states that after receiving the 0x04 or 0x06 command, "all devices designed to respond to the general call address will reset and take in the programmable part of their address." This means that the address present on the hardware pins of the device will be taken in (device own address) internally so that the device knows which address to respond to. 

    1. Does the shutdown mode affect the ALERT pin somehow? 
    Yes, placing the TMP75 in Shutdown mode will clear the ALERT pin. 

    2. Does the temperature register represent the value in two's complement form with the most significant bit as a sign bit?
    Yes, the temperature register value is represented in two's complement binary notation. The MSB, bit D7 of byte 1, is the sign bit.

    3. Do the four LSB's of the temperature value represent the fractional value?
    Yes, the four LSBs from byte 2 represent the fractional temperature value. They correspond to 0.5°C, 0.25°C, 0.125°C, and 0.0625°C.

    Best regards,
    Ian Williams
  • 0 in reply to Ian Williams
    Expert 1870 points

    Does the ALERT pin change it's state on the ONE SHOT measurement?

  • 0 in reply to Anatoly Odler
    TI__Mastermind 27715 points

    Hello Anatoly,

    The TMP75 will shut down all internal blocks except the I2C interface immediately after performing a one-shot conversion, so the ALERT pin will not change state since it requires an internal transistor to turn on and sink current in order to transition from logic high to logic low.

    Best regards,

    Ian Williams

  • 0 in reply to Ian Williams
    Expert 1870 points

    Thank you.

    Anatoly.