# Can I swap Ethernet pairs on UbiSwitch to simplify PCB routing?

**URL:** <https://forum.botblox.org/t/can-i-swap-ethernet-pairs-on-ubiswitch-to-simplify-pcb-routing/650>\
**Category:** BotBlox Hardware\
**Tags:** ubiswitch\
**Created:** [September 19, 2026, 12:51pm UTC](https://forum.botblox.org/t/can-i-swap-ethernet-pairs-on-ubiswitch-to-simplify-pcb-routing/650 "2026-09-19T12:51:02Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![ElsieMichaelson](https://avatars.discourse-cdn.com/v4/letter/e/b5ac83/32.png) [@ElsieMichaelson](https://forum.botblox.org/u/ElsieMichaelson)\
**Post date:** [September 19, 2026, 12:51pm UTC](https://forum.botblox.org/t/can-i-swap-ethernet-pairs-on-ubiswitch-to-simplify-pcb-routing/650/1 "2026-09-19T12:51:02Z")

</div>

_This topic was migrated from the BotBlox ticketing system after being summarized and anonymized._

**Question**

We’re designing a PCB using UbiSwitch’s 1000BASE-T ports and would like to swap Ethernet differential pairs to simplify routing.

Application note BB-AN-0004 describes pair-swapping support. Does this allow any arrangement of the four pairs? For example, could we change the pair order from `ABCD` to `CABD`?

Can we also reverse the `+` and `−` signals within an individual differential pair?

**Answer**

UbiSwitch supports automatic pair-swap correction for 1000BASE-T, but only within two specific groups: **A/B** and **C/D**.

You can swap A with B, and independently swap C with D. You cannot move pairs between those two groups.

**Which pair orders are supported?**

Starting from the standard order `ABCD`, the supported arrangements are:

| Pair order | Change | Supported |
| --- | --- | --- |
| `ABCD` | No swap | Yes |
| `BACD` | Swap A and B | Yes |
| `ABDC` | Swap C and D | Yes |
| `BADC` | Swap A and B, and swap C and D | Yes |
| `CABD` | Move pairs between the A/B and C/D groups | No |

The two permitted swaps are independent, so you can apply either one or both to simplify PCB routing.

**Why is `ABCD → CABD` not supported?**

In `CABD`, pair C occupies a position belonging to the A/B group, and pair B occupies a position belonging to the C/D group.

UbiSwitch’s correction capability does not support this arrangement. It can correct swaps within each group, but it cannot automatically correct an arbitrary permutation of all four pairs.

**How should the pairs connect to the MDI signals?**

Keep the pair groups assigned as follows:

| Ethernet pair group | UbiSwitch MDI signals | Allowed flexibility |
| --- | --- | --- |
| A and B | `MDIP/N[0:1]` | A and B can exchange positions |
| C and D | `MDIP/N[2:3]` | C and D can exchange positions |

When routing, keep A/B within MDI positions 0 and 1, and C/D within MDI positions 2 and 3.

**Can I swap the positive and negative signals within a pair?**

Yes. UbiSwitch supports **polarity correction in 1000BASE-T** , so you can reverse the `+` and `−` signals within an individual differential pair.

This is separate from swapping whole pairs. Reversing a pair’s polarity leaves it in the same MDI position; exchanging whole pairs changes which MDI position each pair connects to.

For routing flexibility, you can therefore use the supported A/B and C/D swaps together with polarity reversal within individual pairs. The A/B and C/D group assignments must still be preserved.