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THVD1552: SPI to RS-422 & UART to RS-485 design solution

Allen yang
Intellectual 545 points
Part Number: THVD1552
Other Parts Discussed in Thread: AM26LV31, THVD1406, AM26LV32E, AM26LV31E, THVD1500, THVD1400

Tool/software:

Hi Team,

Please suggest SPI to RS-422 & UART to RS-485 design solution

No IC specified

Thanks

  • 0
    Guru 297970 points

    For SPI, there are four-channel transmitters and receivers (e.g., AM26LV31/32); you would need to add a one-channel transceiver for the MISO signal.

    In a half-duplex RS-485 bus, a transmitter must have three states (low, high, and disabled for receiving). This usually requires a separate control signal for the DE pin, or a transceiver with auto-direction control like the THVD1406.

  • 0
    TI__Guru 63230 points

    Hi Allen,

    I agree with Clemens on the suggestion for the AM26LV31E and AM26LV32E for the SPI lines as these are our recommended RS422 quad driver/receivers. You will need one additional channel. We usually recommend THVD14XX or THVD15XX for our single channel devices. 14XX is general purpose and 15XX is usually the more cost competitive but lower performance. 

    For UART, you can look at THVD1400 or THVD1500 as a starting point. As Clemens pointed out THVD1406 has auto direction which some customers like to use.

    -Bobby

  • 0 in reply to BOBBY
    Intellectual 545 points

    Hi  Clemens & Bobby,

    Do you have a reference design circuit diagram?

    Does SPI to RS-422 need to use M0 MCU for data conversion?

  • 0 in reply to Allen yang
    TI__Guru 63230 points

    Hi Allen,

    Allen yang said:
    Does SPI to RS-422 need to use M0 MCU for data conversion?

    RS422 isn't a protocol. If you send a SPI signal into an RS422 driver into an RS422 receiver, the receiver will provide the output as SPI again. So you don't need to decode the signal from RS422 to SPI (it's basically done for you if you pair it with an RS422 receiver). 

    Allen yang said:
    Do you have a reference design circuit diagram?

    I don't think we have a reference circuit for this but you would basically just use 3x channels of an RS422 driver for the 3x SPI outputs. 

    I know my drawing is a bit crude but this would be a high level of what it looks like. The top 3x drivers on the left are the AM26LV31E. The top 3x receivers on the right are the AM26C32E. The bottom block with the MISO line would be one of the THVD14XX devices. 

    -Bobby