Why is A at pins 7-8 and not 1-2 as “usual”?
Why is the order of pairs C and D swapped? (it doesn’t even seem to make routing easier, on the contrary)
Why is the order of + and - swapped for pair C?
I would have expected something like :
pin 1 : A+
pin 2 : A-
pin 3 : B+
pin 4 : B-
pin 5 : C+
pin 6 : C-
pin 7 : D+
pin 8 : D-
Is there any reason to follow your (strange) pinout instead of the simpler one?
When designing a PCB, pin order and numbering are usually arbitrary. The goal isn’t to make them “look right” from a human perspective, but to choose an arrangement that maximizes functionality and simplifies routing.
A good example is the RJ-45 connector. In Ethernet, the B pair signals are split across pins 3 and 6 instead of being adjacent. This might look odd at first, but the choice was made for backward compatibility reasons.
On our own hardware, all of our boards use the same pinout for 1000BASE-T wiring. That consistency means we can reuse the same cables across our entire product line. I can’t recall the exact historical reasoning behind the specific pin mapping, but the important point is that it works and it’s consistent.
It’s also worth noting that 1000BASE-T doesn’t inherently “know” or “care” which physical pins carry which signals, as long as each pair ends up connected to the correct pins on the PHY, everything functions correctly.
Changing pinouts
If you’re considering re-arranging the pinout on your baseboard purely to make it appear more logical to a human, it’s generally not worthwhile. There’s no real functional benefit, and it could introduce unnecessary complexity.
That said, if re-ordering pins would make your PCB routing significantly easier, or if you need to match a specific cable standard, then it can make sense. In those cases, function should always take precedence over aesthetics.
We also offer a custom cable service that can accommodate alternative pinouts. However, custom cables do come at a higher cost, so if you can stick with the standard pinout and use the cables we provide, that will usually save you time and money.
