SNLS579A April 2018 – November 2018 DP83TC811S-Q1
xMII Loopback is the shallowest loop through the PHY. It is a useful test mode to validate communications between the MAC and the PHY. When in xMII Loopback, data transmitted from a connected MAC on the TX path is internally looped back in the DP83TC811S-Q1 to the RX pins where it can be checked by the MAC. There is no link indication when in xMII loopback.
xMII Loopback is enabled by setting bit in the BMCR Register 0x0000 – Basic Mode Control Register.