V5 and crossover cables?

VEX V5 General Discussion Technical Discussion
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@Paul Copioli What would happen if someone accidentally used an RJ11 crossover cable in the V5 system? (ignore the RJ11 part in the pic below) Do you have a diagram for us yet?

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Excellent question.
To my best knowledge, the pinout is as follows:

  1. RS-485 A
  2. RS-485 B
  3. Power
  4. GND

So if you manage to get a RJ11 crossover cable somewhere (or actually made one yourself, that’s much more likely occurence) and use it, you should still be good - as in, it won’t work, but nothing will burn.

RS-485 inputs need to be very resilient and high-enough input impedance anyway, so power into one of them is no big deal (the chips I have seen used survive ±70V, besides 16kV static discharge).
RS-485, when signalling logical one over crossover cable would effectively put about 3V reverse voltage on the power pins, something I bet VEX design deals with properly too.

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