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I design my ethernet to RS485 controller board using SPI and does fail EMI pre compliance. The switching frequency on my transceiver is. 800kHz fro WS and 4MHz for SPI configuration which ma de fail the EMI, any suggestion on how to correct it?

Associate III

You could start by posting some captures of your pcb design.

Which EMI compliance test are you failing?

we dont need to firmware by ourselves, lets talk
Associate III

We are talking abour EN55011 Class radiated.

Joined is the result of EMI-Test.



Associate III

How many layers did you used in pcb? Do you have a solid ground plane under signals?

Associate III

I am using 6 Layers build as follow:

Yes Layer 2 is filled completely with GND Polygon


6 layer PCB is way out of my leage, i hope someone else can help.

Do you have any hint about where the problem could be?

I dont see any GND via stiching ,is that intentional?

Do you have any high speed buses/power switches/radios/ LED or motor driver/ in your board?

Did you split ground planes?

we dont need to firmware by ourselves, lets talk


Any Hint: The data send to the transceiver are with 800kHz oder 4MHz and this data is converter to a dfferential signal which is send through the ethernet connector RJ45. This noise is coming from this send path. I thought may be adding a serial capacitor at the termination resistor may help solve the problem, any idea?

The data send from the µC to the transceiver and from Transceiver to RJ45 is for LED control which as stated control with either 800kHz or 4MHz.

I will be delighted for your feedback