IMXRT CUSTOM ETHERNET PHY NOT WORKING

[nicolasmuratore]

Hi all, hope this email finds you well, I'm trying to develop a custom board using IMXRT1021DAG, this board has an ethernet interface based on the same ethernet interface of the EVK.

In fact I'm using the same PHY KSZ8081RNB, and the circuit is almost the same of the EVK too (I didn't put the pull ups resistors on the analog side because those are implemented inside the PHY):  

The only difference is the RJ45 connector, I'm using Thru hole (WURSHT 7499010211A) against the SMD of the EVK, just for robustness, but the internal transformers and parameters are the same:

I'm using an example of the SDK that allow me to test the interface sending frames and then reading them back, using a loopback cable connected to the RJ45 that is working perfectly on EVK.

Problem: The test is not working on my board, the PHY doesn't send any frame to the analog side (RJ45 side).

I know that the communication between the MAC (IMXRT1021) and PHY is ok because I can do a digital loopback test (available on KSZ8081RNB to test RMII communication).

I tried to test doing the following connection too:

My board receive all the frames, sent from EVK, in right way, but in the moment of transmiting from custom board to EVK, the MAC send information over RMII channel but PHY doesn't send any frame to the other side.

I've checked the PCB, the components, the routing of RJ45 is similar to EVK, keeping differential pairs togueter and impedance low 100Ohm. 

I really don't understand what is happening, any idea would be very appreciated.

Many thanks. 

[Hui_Ma]

Hi,

From the problem description, the only difference at Ethernet circuit design is the PHY.

And customer board could receive data frame from EVK board sent.

Besides of PHY circuit and soldering review, please check the Ethernet cable status.

Mike

[nicolasmuratore]

I did some test and realized that many packets are missing during reception on my custom board from the EVK transmission, so I was wrong on my first post when I said that the reception was ok.

I think that maybe the problem is related to signal levels or signal detection on the RJ45 side.

I've checked the circuit and components from RJ45 side (there are not many really, just two capacitors and the connector) and everything semms to be ok, I have soldered the KSZ8081 again.

So, what could be wrong?

Is a mistery by now. 

Many thanks.

[Hui_Ma]

Hi,

How many boards have you tested? All with the same issue?

Mike

[nicolasmuratore]

Hi Mike, I've tested 6 six  boards with the same issue, I have almost 20 prototipes, so I will continuing cheking all of them to find something related to the PCB construction, welding, etc.. 

I really can't think in another thing that is not related to PCB manufacturing.

Many thanks.

[Hui_Ma]

Hi,

Besides of hardware soldering, please check the PCB layout design also, especially for ENET PHY connection with RJ45 connector. Thanks.

Mike

[nicolasmuratore · Accepted solution]

I found it!!!

One of the resistors that controls the output power, with a value that should be 6.49K, is wrongly 64K, so the output didn't have enough power to transmit signals, my components supplier made a mistake.

Now is working, besides that I solved some welding problems too.

Many thanks for your guidence on this issue.

[Hui_Ma]

Great!

You are welcome. Nice to know this issue was fixed. 

Mike

[nicolasmuratore]

Hi Mike, thanks for your answer, I will check all the connections again, then I will let you know.

Many thanks!!!