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

Marko Siponen
Prodigy 20 points
Part Number: TMP126-Q1
Other Parts Discussed in Thread: TMP126

When exactly does the SIO pin change from input to output?

The data sheet only says "During a read command the TMP126-Q1 will control the SIO pin after the command word."

It doesn't state exactly when after.

Is it immediately after clocking in the 16-th bit of the read command word or does it change when it transmits the first bit of the data block?

  • 0
    TI__Expert 6295 points

    Hi Marko,

    The TMP126-Q1 will control the data line after the command word is sent--granted that R/W bit is set to 1 by the controller. 

    This will not happen at the fist bit of the data block due to the timing of SPI communication. Are you having issues with the delay between words after the command block? 

    Best regards,

    Simon Rojas 

  • 0 in reply to Simon Rojas Avila
    Prodigy 20 points

    I noticed that the SIO signal to the TMP126 has slow rise/fall time because of the 10k resistor there. So I could only run at about 500kbit/s.

    So I tried to run without the 10k resistor and instead turn off master MOSI after sending the read command (to not conflict with data sent from SIO).

    This way I can run at 8MHz.

    I just wonder how much time there is after sending the read command word until the slave controls the SIO pin. If the master is too slow to turn off MOSI there could be a conflict of logic levels on SIO. I could solve this by again adding the resistor but using a much lower value.

  • +1 in reply to Marko Siponen
    TI__Expert 6295 points

    Hi Marko,

    Thank you for clarifying. Running the communication at 8MHz is ok from the device perspective as the datasheet specifies a maximum communication frequency of 10MHz.

    To your question, the falling edge of the 16th bit of the command word is what triggers the device to control the communication line. Not using the resistor is ok as this is a push-pull interface--as long as the controller can switch fast enough. In short, your max speed will be determined by how fast your master can HI-Z the MOSI line.

    Best regards,

    Simon Rojas