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THVD2410V: Typical circuit for RS422

Brian Li
Expert 8685 points
Part Number: THVD2410V
Other Parts Discussed in Thread: THVD2412V, THVD2452V

Hi team,

My customer is using our THVD2410V whose datasheet says it can also support RS422.

So could you please kindly help check if we have a typical circuit for RS422 with our THVD2410V to share with the customer?

Thanks,

Brian

  • 0
    Guru 257100 points

    To simplify, RS-422 is just unidirectional, point-to-point RS-485. So one transceiver always has the driver enabled, the other transceiver always has the receiver enabled, and only the receiver needs a termination resistor. Also see this short presentation.

  • +1
    TI__Mastermind 45417 points

    Hi Brian,

    So while you can use the THVD2410V for RS-422 you probably would be better off using the THVD2412V for RS-422 (its in the same datasheet and currently in preview - I believe we may already have EVM's available as well). Reason being is that RS-422 systems are full duplex (its multi-drop; 1 host talks to up to 10 peripherals where the transmission pair of wires connects to all peripherals and its receive pair of wires is connected to every peripherals transmission pair of wires. Here is a simplistic RS-422 example:

    This shows two receivers - with only 1 communicating back to host device. 

    G is represented by Y/Z pins on THVD2412V

    R is represented by A/B pins on the THVD2412V

    Here is a one a little more tied to TI's style:

    This is in data-sheet - but shows termination setup for RS-485 (which has termination on driver and receiver in full-duplex mode). 

    R term = 100 Ohms (RS-422 standard) Only terminate the last receiver on the bus and terminated the RX pair on the host device. 

    You can use the THVD2410V - but generally you will need to 2 of them per node (one in TX mode and one in RX mode) - they are electrically compliant with RS-422; but from a system configuration point of view you need more devices than if you were to just use a full duplex device. This is because if all devices are are on one half duplex bus - you are no longer in a multi-drop system (as RS-422) but in an multi-point system (such as RS-485 (485 can also do multi-drop as well)) so that's why'd I try to steer your customer to a full-duplex option. 

    For logic pins - its the same setup as shown in datasheet for both RS-422 and RS-485. This device can only get to 1Mbps without slew rate limiting - so if you need higher data rates the THVD2452V is essentially just a faster version that can switch between 20Mbps and 50Mbps. 

    If they absolutely need to use the THVD2410V then from the second picture I shared each node will need 2 devices for proper RS-422. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson