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TMP107-Q1: Communication start timing after initialization process

Takahiro Saito
Expert 5335 points
Part Number: TMP107-Q1
Other Parts Discussed in Thread: TMP107

Hi team,

My customer is using two TMP107-Q1 with daisychain configuration for digital signage.

The datasheets describes about the initialization in 8.3.3.2.1.1 like bleow.

"Until the initialization process is completed, daisy-chain communication is directed toward the host. Do not send any new commands to the chain during this period."

How much time does the host need to wait until starting a communication after the initialization process? Customer confirmed that TMP107 didn't response when the host send the command to TMP107 just after the host receives the address response from TMP107 at the end of daisychain. But, when customer wait 30ms-50ms after the address response, TMP107 could respond.

So, could you check what timing can the host start the communication after the initialization process?

Regards,

Saito   

  • 0
    TI__Guru* 91166 points

    Dear Saito - 
    Thanks for posting - the amount of time will depend on the number of sensors in the chain.

    The method for determining how long will be derived from the baud rate of the bits sent out and received back from the sensors, plus 7mSec interval between each sensor in the chain. See Figure 23 (on the same page you see the wording you asked about , page 18)

  • 0 in reply to Josh Wyatt
    TI__Expert 5335 points

    Hi Josh-san,

    Is the communication available as soon as the host received the address response from all devices in the chain?

    Customer said they had to wait 30ms-50ms after the host received the address response from all device in the chain.

    I think how long the host have to wait doesn't depends on the baud rate and 7ms in figure 23.

    Regards,

    Saito   

  • +1 in reply to Takahiro Saito
    TI__Mastermind 39045 points

    Hi Saito,

    Each device is writing address to EEPROM during Address Init. The datasheet states that it takes 7ms to write to EEPROM. It will take at least 7ms * device count to complete the Address Init command. Since the devices in the chain must wait until all devices have responded to the Address Init command, they are configured to transmit towards the host. It could take up to 1.25s to complete Address Init for a complete chain of 32 devices. After the last response is received, the Communication Timeout of 35ms takes effect. The devices will change direction to transmit downstream. When this happens, they are ready for a new transaction.

    Please note that Global Address Init should only be performed once on new hardware, or when the chain has been physically altered. If you need to check the chain at power-on, you should use Last Device Poll instead. This will tell you the size of the chain for use in Global Commands. If the Global Address Init is performed at every power-on, the EEPROM will wear out.

    thanks,

    ren

  • 0 in reply to Ren Schackmann
    TI__Expert 5335 points

    Hi Ren-san,

    Thanks. I understand the host needs to wait for the device timeout time before the host send a command again.

    Regards,

    Saito