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TMP123: By pulling CS high, conversion always starts?

user5047997
Prodigy 30 points
Part Number: TMP123
Other Parts Discussed in Thread: TMP121

Let me ask about the relation between CS control and conversion time.

Datasheet of TMP123 describes the followings,

At "COMMUNICATING WITH THE TMP121" of APPLICATIONS INFROMATION in page5

  "The TMP121 and TMP123 continuously convert temperatures to digital data while CS is high. "

  "CS must be high for a minimum of one conversion time (320ms max) to update the temperature data."

The chart of electrical characteristics in page3 indicates

  "conversion period is 640ms max", "Period indicates time between conversion starts."

From these, I recognized that A/D conversion in TMP123 ends until 320 ms max, and output SO from TMP123 until 320 ms max.

We determined to set the period of CS signal as 640ms, and 320ms for the duration time.

However, we also confirmed that the last sentence of "COMMUNICATING WITH THE TMP121" describes "A new conversion begins every 0.5s."

This statement makes us confuse if the conversion time can not be operated by external CS control(signal).

Can we also understand that a new conversion begins every 0.5s in TMP123 in the condition that CS pulled up high?

  • 0
    TI__Mastermind 35775 points
    Hi user,

    While CS is high, the TMP will start an A/D conversion every 0.5s in order to keep the temperature information up to date while also conserving power.

    While CS is low, the temperature information will not be updated. This is to prevent corruption of information that is currently being read back.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Prodigy 30 points

    Hi Ren,

    Thank you for your answer.

    I understand the behavior in the case of setting CS fixed high and low.

    Let me ask tow additional questions.

    1, When CS goes down after high period with 0.25s, A/D conversion finished and we acquire updated information.

        After that, when CS goes up again, does the A/D conversion resume soon. We would like to confirm the

        A/D conversion can be restarted by CS control without waiting for another 0.25s.

    2, What happend if CS period exceeds 640ms? Does it influence to the accuracy of data in this case?

  • 0 in reply to user5047997
    TI__Mastermind 35775 points
    There's two shift registers inside which store the temperature information.

    One is used by the A/D during conversion. The other is accessed by serial interface. When CS is Low, the data in the first will not be transferred to the second. When CS returns to High, data can be transferred from the first shift register to the second one immediately.

    This mechanism ensures there is no loss of information or accuracy under the conditions you described.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Prodigy 30 points

    1, If CS goes down Low during A/D conversion (under 0.25sec), is the second resister updated to the mid-flow proceeding data or  kept previous data?

    2,In our understanding, the period of CS = L doesn't need to have more than 0.25sec.

    For example, it is acceptable the case of CS=H is 0.25sec, and CS=L is 1.6us permitted minimum read time (100ns * 16bit = 1.6us). It means the external controller can get newest data every 0.25sec + 1.6us.

    In other word simply, can A/D conversin be restartd by every the positive edge of CS ?

  • 0 in reply to user5047997
    TI__Mastermind 35775 points
    The previous data is kept.

    A/D conversion is not affected by CS. The contents of the second shift register is affected by CS.

    Thanks,
    Ren