I've got two ethernet ICs that should be put back to back with reverse MII mode. For this, I should cross the TX and RX pins and the application note of the reverse MII chip says, the TXER and RXER pins should also be crossed.

The problem is just, that the reverse MII PHY offers the RXER pin but the normal MII chip (LAN9500AI) doesn't offer a TXER pin. Since I couldn't find anoymore information for the LAN9500AI: Should I connect the RXER pin to another pin of the LAN9500AI or leave it open?



RXER is there to tell the receiving MAC that the PHY has seen an error and couldn't decode the data on the Ethernet cable. Since you won't be having any errors on your no-PHY setup, you can just tie it low.

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  • \$\begingroup\$ I should tie it low? It is mentioned as a "MII/RMII receive error output" so it wouldn't be a good idea to fix this output pin... \$\endgroup\$ – martin Oct 12 '15 at 12:56
  • \$\begingroup\$ I haven't bothered to look up your parts and work out what's what, but it it's an output, then no, just don't connect it. If it's an input, tie it low. Either way you don't need to worry about it. If you're really not sure, pull it down through a 10k resistor, then it won't matter either way. \$\endgroup\$ – user1844 Oct 12 '15 at 22:07

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