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40' I2C Bus

Bernard Drew
Prodigy 20 points
Other Parts Discussed in Thread: TXS0104E, TCA9517, TCA9545A

We are using a TXS0104E to communicate with the I2C pins on forty  MSP430s. The MSP430s are  distributed evenly over 40 12 inch pcbs hooked in tandem.   We have added 4.7k terminations resistors at the end of the SCL and SDA lines.  

Will the TXS0104E suffice or is something more elaborate, such as line drives and receivers, advisable?

Thanks

Bernard Drew

  • 0
    TI__Mastermind 30260 points

    The TXS0104E is a 4-channel voltage translator, and voltage translation isn't explicitly mentioned in your description. I am not sure how it fits into the system since I2C is a 2-wire communication protocol.

    It may be wise to use a 4-channel switch like the TCA9545A to isolate 3 MSP430s at a time. Some designers would also put a pad for a buffer (such as the TCA9517) on each slave channel of the TCA9545A in case additional driving capabilities are needed.

    In this scheme, you can wire around the TCA9517 with 0-Ohm resistors in series that would be populated in the original design and you can test your system. If communication fails, the TCA9517 devices can be populated and the 0-Ohm resistors de-populated.

    Also, it is common practice to refer to the 4.7k resistors as pull-up resistors as opposed to "termination" resistors, as termination resistors are connected to GND and not a voltage reference.