WIZnet Developer Forum

W5500 does not bring physical link with some routers


My device with W5500 does not bring physical link with some routers. It turns on yellow LED (LINKLED) for at about 1.5 seconds, then, at the moment of turning it off, turns on green LED (ACTLED) for 0.5s. After it no LED’s activity during 2-3 seconds, and cycle starts again. The situation with different devices:

  • Tp-Link router: connect immidiately
  • Direct to PC (symmetric cable): connect after 0-4 cycles
  • Zyxel Keenetic Omny, another unknown router: infinite cycle, no connect. In 1 way out of 20 connects immidiately.

Sometimes connection to Zyxel can be estabilished after plugging the cable after 10-20s of device start. I use standart schematics (see attach), inductance is 33uH. Zyxel router works stable with PC’s.

Do you know, what W5500 “is doing” at that time and why doesn`t connect?

I was dealing this such issue several times, and my conclusion was that the dumber router device is, the better. W5x00 is being handled by Cisco routers even worse than in your case.

IMHO “too clever” router tries to understand what is on the other end. I do not know what it does exactly, probably performs some electrical training of the lines or sends some diagnostic packets, but for some reason W5x00 family goes crazy about it - they start to reboot or just turn receive LED on (as there would be a packet storm).

In my opinion you have little to do about it from W5x00 side, but you can dig into router config to turn its smartness off.

Well, of course there’s a possibility that your W5x00 device is not working properly, but you would be able to figure it out if you have two or more devices. Then, that your design is not good - then you can figure it out using some standard design from WIZnet or partners seeing how it performs in your environment.

I’ve found only one solution to the problem: put W5500 into 10Mbit mode. It has been done in hardware with ground-connecting of the corresponding pins. Please mark the topic as half-solved.


I have the same problem my w5500 just work with TP-LINK adsl modem !!

you mentioned that we should connect corresponding pins to the ground!, could you please tel me which pins are corresponding?!

thank you

You can override the hardware configuration via software during initialization if you use the ioLibrary. I believe the official recommendation is to connect PMODE0 - PMODE2 to MCU output pins so that you can set them any way you want.

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