||Receive Error Counter
When a valid carrier is presented (only while RXDV is set), and there is at least one occurrence of an invalid data symbol, this 16-bit counter increments for each receive error detected.
The RX_ER counter does not count in MII loopback mode.
The counter stops when it reaches its maximum count (FFh). When the counter exceeds half-full (7Fh), an interrupt is generated. This register is cleared on read.