Ethernet Link

Question

Hi All,

I have come across a very strange problem with ethernet board which has National's 83848M (Fast Ethernet) phy. When I connect this board with PC having Gigabit ethernet NIC or 10/100 Switch/Hub, 100 Mbps link established straight away. But when I connect same board with PC having fast ethernet NIC, link could not be established and nothing happens! I tried to get solution by giving reset to phy explicitly, but problem is not solved.

Has anyone come across same problem?

Your quick help would be highly appriciated! Thank you.

altera_forum · Answer

Do the ethernet phys and transformers have an auto mdix system? If non of them have, you may need to use a crossover cable.

altera_forum · Answer

Thanks Daixiwen! I know PHY has auto mdix, but I am not sure how to check whether transformer has it or not. And of course I know, I need to use crossover cable for point-to-point communication.

altera_forum · Answer

An Ethernet transformer that is auto-midx compatible has the same circuits on the TX/RX pairs, to ensure that they can be switched by the PHY. But as you are already using a crossover cable, the problem doesn't come from mdix anyway.

Do both ends have autonegotiation enabled? For the PC you can change this in the network driver settings usually, and for the PHY you must look for the correct MDIO registers. You could try disabling the autonegotiation and force both ends at 100Mbits/s.

altera_forum · Answer

Yes, both end has auto-negotiation enabled. I tried by forcing at 100 Mbps but result is same. I have order new magnetic which is most compatible for 83848M phy, but if any one has come across this type of situation then please let me know how to solve it.

altera_forum · Answer

I have come across some compatibility issues with certain Phys and auto-negotiation.

It might be worth testing the setup with your fast (100M) ethernet PC but set both ends to the sme speed AND duplex. i.e. try with them both forced to 100M and Full Duplex.

This could narrow the problem down to whether it is a signal integrity issue or an auto-negotiation compatibility issue

Rgds

Vern

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Ethernet Link

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