At Relaxkit 4500 Ethernet TX wires interchanged

Tip / Sign in to post questions, reply, level up, and achieve exciting badges. Know more

cross mob
User7795
Level 4
Level 4
Hi Infineon,

at Relaxkit 4500 Rev1.2 the TX connections from phy (IC200) to RJ45 (X200) are interchanged, TXP is connected to TD- and TXM to TD+. Please is there any reason for or is this an error?

Best Regards
Wolfgang
0 Likes
2 Replies
jferreira
Employee
Employee
10 sign-ins 5 sign-ins First like received
Hi,

I would advise to follow Design Checklist at https://www.microchip.com/wwwproducts/en/KSZ8081.

Regards,
Jesus
0 Likes
User7795
Level 4
Level 4
Hi Jesus,

thanks, the checklist says:
"MDI Connections: Pin 1 of the RJ45 is TX+ and should trace through the magnetics to TXP (pin 7) of the KSZ8081RNB. Pin 2 of the RJ45 is TX- and should trace through the magnetics to TXM (pin 6) of the KSZ8081RNB."

So there is no reason to interchange the tx connections.
But TX+ connected to TXM and TX- to TXP only results in a phase change by 180 degr, at clock frequency of 125 MHz (100 MBit/s) and a wavelength of about 2 meters in the cable it's like a cable length difference of 1 meter between tx and rx line. This doesn't affect the clock recovery in the phy, it will compensate this phase difference, so this 'wrong' connection also runs.

Best Regards
Wolfgang
0 Likes