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PGA460PSM-EVM: Is there possibility of interference from TXD pin with multiple boards on a single bus?

Kajetan Dworski
Prodigy 170 points
Part Number: PGA460PSM-EVM
Other Parts Discussed in Thread: PGA460

Hello,

We are working on a project using four PGA460PSM-EVM boards and are wiring them up on a single bus so we can communicate with them via UART.

A question arose whether there is a possibility of interference from other boards from their TXD pins when one of them is transmitting and whether we should add circuitry to mitigate this. Is this already accounted for by the PGA460 design? Is it something to take into consideration when we design our own boards using the chip?

Regards,

Kai

  • 0
    TI__Mastermind 27950 points

    Kajetan,

    When using multiple PGA460 devices on the UART/SPI bus, it is important to note that the UART_ADDR value of each device must be different so there is no interference/collision of PGA460 data. Refer to PGA460 FAQs # 2.4 and 4.4.11 for more details: http://www.ti.com/lit/an/slaa733/slaa733.pdf

    2.4 How can I prepare for mass production programming and system integration?

    4.4.11 Is daisy-chain supported by the PGA460? Can the master controller automatically differentiate and program the PGA460 UART address?

  • 0 in reply to Akeem Whitehead
    Prodigy 170 points

    Hi Akeem,

    I understand the need for the different addresses.

    What I wanted to know is on the circuit level - when a PGA460 transmits it pulls down voltage on the TXD pin from HIGH to LOW to send its binary data. When it's daisy-chained with other boards, is there a possibility for the HIGH signal from other boards will interfere with the transmission, ie. is there any chance the data will be corrupted.

    We have an idea for a circuit to ensure this has no chance of happening, but we wanted to check if there isn't already an implementation within the chip to handle this and I couldn't find anything explicitly mentioned in the documentation.

    Kind regards,

    Kai

  • 0 in reply to Kajetan Dworski
    TI__Mastermind 27950 points

    Kai,

    I have not encountered this type of communication interference when implementing a UART/USART/OWU bus of up to eight PGA460 devices.

    The PGA460 TXD pin is always in a tri-state mode during the idle communication (slave is not responding) state. In UART mode, the PGA460's TXD pin expects the master's RXD pin to implement a weak pull-up; otherwise, the PGA460 will only force a logic 0 or 1 while responding.

    Here is a post that may of interest to improve TXD pin robustness with an external or master pull-up resistor on the PGA460 TXD pin: : https://e2e.ti.com/support/sensors/f/1023/p/840688/3201553#3201553