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We received a piece of equipment (actually from an Italian manufacturer, if that gives a hint) which uses RS-485.

So, as well as a power connection the devices have THREE WIRES (bare wires) coming from the relevant board, being white, gray, black.

We have all the custom communications protocol in a PDF, but they neglected to include a mention of the wiring of the RS-485.

Can you guess which is A, B, Reference?

Is there a typical color scheme for the three, for "raw" 485 wires?

As it happens the engineers are completely on holiday for a week! (Typical production hang-up right?) Also just generally curious if there is a typical standard for this.

Just FTR if relevant, the plan by us and them was that the three wires would connect to a convertor to RS-232 and hence to an ordinary (ie Windows8) PC; cable lengths are only a meter or two.

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  • \$\begingroup\$ Can you trace them to a chip? \$\endgroup\$
    – Ignacio Vazquez-Abrams
    Commented Jun 1, 2015 at 4:07
  • \$\begingroup\$ Ignacio -- Not quite, just to the connector on a board. In any event, I was curious if there is a typical color scheme here. \$\endgroup\$
    – Fattie
    Commented Jun 1, 2015 at 4:10

1 Answer 1

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Joe - forget about hopes of finding a standard color scheme.

The simplest thing is that the Reference (Common) lead will connect to the GND of the circuit. That should be dead simple to discover which one with a multi-meter.

Finding that the other two will be the A and B lines. Hook those up one way and see if any protocol makes sense. If not then hook them up the other way.

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  • \$\begingroup\$ Thanks Michael, looks like the definitive answer. Cheers. \$\endgroup\$
    – Fattie
    Commented Jun 1, 2015 at 12:25

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