Interfacing an Ethernet switch with STM32F417 - What to do with the TX_ER signal?

[EKarg.1]

Hello.

In my design, I need to communicate the MCU on my board with two other boards by using Ethernet connection. For this purpose, I am planning to add the Ethernet switch IC LAN9313 in my design.

In the reference design document (given by Microchip), the MII signals are listed as follows:

 

The microcontroller expects these pins (the green ones) to be connected to it.

 

Okay, they perfectly match, but expect for the TX_ER signal. The MCU doesn't have any pin for this signal. The Wikipedia page says that this signal is optional. Can you please shortly explain the importance of the TX_ER signal. If I am allowed to leave it unconnected, what could go wrong in my design?

Thanks in advance.

[Muhammed Güler]

MII Transmit Error: Indicates a transmit error in the packet.

•In MAC mode, this signal is output to an external PHY and indicates an invalid symbol is to be transmitted. This signal is always driven low when in MAC mode. See Note 3-3.

•In PHY mode, this signal is input from an external MAC and indicates the current packet should be aborted.

Note 3-3When used as an output, the pin(s) input buffer(s) and pull-down(s) are disabled

it looks like it can be left unconnected.