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AM26LV31 and AM26LV32 arranged in half duplex topology

Other Parts Discussed in Thread: AM26LV31, AM26LV32E, SN65HVD75, AM26LV31E

Hello,

I have a quite complex RS422 interface, with three inputs, one output and two bidirectional lines.

As AM26LV31 and AM26LV31 are good for all my timing requirement, I was thinking about using them for this application, but in order to use them for the bidirectional lines, I should arrange them in a half duplex topology (I would also need one more receiver, but that's not the problem at the moment).

From the output schematics of AM26LV31 I see it has push-pull drivers, which brings me to think there is no way to reach my goal, as the AM26LV31 output will always be driven and so I would only create a loopback with the two parts. Also, temporarily disabling AM26LV31 outputs when using the interface in the other direction is not an option, because the other output signals should be used together, and AM26LV31 only has a general enable pin, valid for all four outputs.

That said, is there something I missed or some alternative solution I could use in order to use them together this way? I should also say that the bidirectional lines refer to two different alternative modes of operation, which cannot be used at the same time (this maybe helps...).

Thanks in advance.

Regards,

Stefano

  • Stefano,

    For the three inputs, AM26LV32E is recommended. 

    For the two bidirectional lines, I suggest two SN65HVD75. 

    One of the SN65HVD75 can double as the one RS422 output

    RS422 driver don't work well for bidirectional data. One reason is that termination is needed at both ends of the cable which is too much load.

    Also RS422 driver outputs do not allow negative voltage even when off.

  • Hi Ron,
    yes, I missed the final "E", but I was referring to AM26LV32E (and its companion AM26LV31E).

    About RS422, I did not consider terminations and negative voltages, so your help is much appreciated.

    Thanks,
    Stefano