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on my system I need to connect two devices together, these devices have an RS422 interface and a DI2C interface (differential i2c, PCA9615 driver). Both RS422 and DI2C need 2 pairs.

The question is: is it possible to use only one ethernet cable for both RS422 and DI2C? (two pairs for RS422 and two pairs of the same cable for RS422)? Or is it better to use two separate cables?

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    \$\begingroup\$ Do you need a ground reference between the boards through your cable, or do the boards already share a ground reference via some other path? \$\endgroup\$
    – Justme
    Commented Jul 19, 2023 at 11:25
  • \$\begingroup\$ I need ground. The two interfaces share the same ground. I was thinking of using the cable shield as ground between the two boards. \$\endgroup\$
    – Federico Massimi
    Commented Jul 19, 2023 at 11:27
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    \$\begingroup\$ OK, and when you mean Ethernet cable, do you mean the ones with 8P8C modular jacks, or will you just be using shielded CAT5 with custom connectors? \$\endgroup\$
    – Justme
    Commented Jul 19, 2023 at 11:35
  • \$\begingroup\$ How long does your cable need to be? \$\endgroup\$
    – jonathanjo
    Commented Jul 19, 2023 at 11:42
  • \$\begingroup\$ @Justme: Yes, CAT5 with custom connector. \$\endgroup\$
    – Federico Massimi
    Commented Jul 20, 2023 at 7:10

1 Answer 1

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If you use a cable with 4 pairs, there are no wires left for ground reference or return wire between devices.

The shield is generally intended to be used only as a shield, not a ground conductor that can carry currents between devices.

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  • \$\begingroup\$ SO better use, 2 separate cable 2xTwisted wire + 1 single wire for GND? \$\endgroup\$
    – Federico Massimi
    Commented Jul 20, 2023 at 7:11

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