The RTL8309M-CG is a 9-port 10/100M Ethernet switch controller that integrates memory, nine MACs, and eight physical layer transceivers for 10Base-T and 100Base-TX operation into a single chip. It supports a (T)MII/RMII interface for external devices to connect to the 9th MAC. The external device could be a routing engine, HomePNA, HomePlug, or VDSL transceiver depending on the application. In order to accomplish diagnostics in complex network systems, the RTL8309M provides a loopback feature in each port.