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TMP144: Reading Time for 12 Daisy Chain

Part Number: TMP144
Other Parts Discussed in Thread: TMP107, TMP104

Hi team,

My customer needs to know the time needed to read 12 daisy chain by one-shot reading.

Datasheet mentions that individual read can take place in less than 300 μs.

Does it mean reading time of 12 daisy chain will be 3.6ms?

Does TI have formula to estimate reading time of multiple daisy chain?

Regards,

Itoh

  • Itoh-san,

    The below information is actually for TMP107. It will be very similar for TMP144. Let me figure it out and post again with the correct analysis for TMP144.

    See Figure 29 of the datasheet. The global read command is 3 bytes, and is followed by 2 byte responses from each device in the chain. The timing estimate is: (1/baud) * (3*10 + (1.5+2*10)*N) seconds. 

    At the max baud rate, and 12 devices, the calculation is: (1/115400) * (3*10 + (1.5+2*10)*12) = 2.5ms minimum, estimated.

    Here's an oscilloscope picture of 3 devices at 57600 baud. The estimate for this communication is (1/57600) * (3*10 + (1.5+2*10)*3) = 1.64ms. It was measured at 1.66ms.

    thanks,

    ren

  • Hi Itoh-san,

    TMP144 and TMP104 uses only one command byte where TMP107 uses two.

    The devices respond with two bytes each in TMP144 (same as TMP107,) or one byte each in TMP104. 

    The delay between responses is 1 baud in TMP104/144 as opposed to 1.5 baud in TMP107.

    The max baud for TMP104/144 is 114000 compared to 115400 in TMP107.

    For TMP144, the correct estimate is:  (1/114000) * (3*10 + (1+2*10)*12) = 2.47ms

    For TMP104, the estimate is:  (1/114000) * (3*10 + (1+10)*12) = 1.42ms

    thanks,

    ren