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Original question:

TMP126-Q1: When exactly does the SIO pin change from input to output?

TMP126-Q1: Data available when switching from write to read

Martin Knoetze
Prodigy 20 points
Part Number: TMP126-Q1
Other Parts Discussed in Thread: TMP126

Tool/software:

A follow-up question on the turn around between write and read to/from the TMP126.

The previous tread said that the turn around between write and read is on the first falling edge after the last write bit has been clocked into the device. On which falling edge is the first read data bit available:

- On the same falling edge when the switch around between write and read happens, or

- On the the following falling edge.

I would assume it is on the same falling edge when the turn around between write and read happens.

  • 0
    TI__Mastermind 39225 points

    Hi Martin,

    I've highlighted the area where TMP126 drives the SIO pin on read transactions. this is also reflected in the shading of Figure 8-13, 8-14, and 8-16.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 20 points

    Hi Ren

    The Figure 8-9 and the other figures do not provide the answer I want as they do not show any relationship between SCLK and data in/out.

    The description in 8.5.2 is helpful in providing the info when data is clocked in/out. But what is nowhere to be found in the datasheet, is the SCLK edge relationship between command data being written and data being read - that crossover condition. 

    I'll ask again - when does the first read data bit appear on the data line compared to the last command bit being written into the device. Nothing in your datasheet gives that info. Just based on the description in 8.5.2, the first read bit can appear on the 1st or 2nd or n-th falling edge after last command bit has been written in on the 16th rising edge of SCLK. That is the info I'm looking for.

    My assumption is that the first read data bit appears on the first falling edge of SCLK after the rising edge of SCLK that clocks in the last command bit. But that info is not in the datasheet. And assumptions are not good in this case.

    Regards

    Martin

  • 0 in reply to Martin Knoetze
    TI__Mastermind 39225 points

    Martin,

    The SIO must change direction on the falling edge of the last "command" bit. The TMP126 does not know when the next rising edge will occur, and must be prepared for it. This is why the text says "Data is clocked out on the falling edge of the serial clock."

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 20 points

    Yes I know already that SIO changes direction at the falling edge of the command bit.

    You are NOT providing me with the answer I'm looking for. Please read my question properly. I'm going to repeat it here in a slightly different form.

    Once the SIO direction has changed, WHEN DOES THE FIRST READ DATA BIT APPEAR ON THE TMP126 SIO OUTPUT. Does it appear on either of:

        - The same falling edge that SIO changes direction, or

        - The next falling edge after SIO has changed direction

    Regards
    Martin

  • 0 in reply to Martin Knoetze
    TI__Mastermind 39225 points

    Hi Martin,

    The first bit appears on the same falling edge that SIO changes direction. The figure shows 16 clock pulses per data word; there are no wasted clocks.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    Prodigy 20 points

    Hi Ren

    Thank you. That answers my question on the TMP126 and I think I'm good to go on it now.

    Martin