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How to buffer RS422 signals

Yifu Chen
Prodigy 120 points
Other Parts Discussed in Thread: AM26C32, THVD1512, AM26C31

I am using a RS422 ABZ encoder and need to transmit this signal to two receiver, for example, a motion controller X and maybe a DSP Y. There are distance between them(encoder, X and Y).

I have two solutions 

#1 is just to seperate these signals on a PCB, and there is no chip. My concern is impedence(reflection) and noise(Because there are motors nearby) 

#2 is to have use buffers on a PCB. I cannot find buffers for RS422 but I found TTL buffers. I use a RS422 signal into single-end first and buffer it out into 2 channels. Then I use two RS422 transmitters. In this case, my concern is signal delay

Anybody did anything similar before or have any ideas on how to do this? Many thanks

  • 0
    Guru 283200 points

    If you can route the signal from the encoder to X, and then from there to Y, then you do not need any buffer:


    (source: Wikipedia)

    But if you have separate cables to X and to Y, then you should use a buffer. This is needed only where a cable branches off from the main bus; the main bus can continue without a buffer. (And you do not need an actual logic buffer; you can connect the receiver's outputs directly to the driver's inputs.)

  • 0 in reply to Clemens Ladisch
    Prodigy 120 points

    Thank you so much. I need to separate calbles to X and to Y. Do you know if there are any RS422 buffers? Or I can only use RS422 receiver and trasmitter instead? 

    Yes my bad. Buffers are not actually needed.

  • +1 in reply to Yifu Chen
    Guru 283200 points

    You have three signals, so you need three full-duplex transceivers (e.g., THVD1512) with R connected to D, or a multichannel receiver and a multichannel driver (e.g., AM26C32/AM26C31).