AM5706: RMII communication issue

 Now we  can get DP83848 phy ID,whicn indicates that MDIO communication is successfull,but when ping the pc through  UART3 DEBUG SERIAL port ,there is  no data on txd0, txd1, and  txen .but there is data on rxd0,rxd1 and rxer .why? what register should be modify?

DP83848J.pdf