Network interface system and method for dynamically switching between different physical layer devices

A system and method for dynamically switching between different physical layer devices (PHYs) in a network interface. The system comprises a network interface in a network device, e.g., a network card in a computer system which includes a first PHY device and a second PHY device. The first PHY device is coupled to a first transmission medium (such as fiber-optic cable) which requires a continuous connection to the computer system when active. For a SERDES device, this continuous connection is required because the PHY needs constant access to its physical coding sublayer (PCS), which is located external to the PHY. The second PHY device is coupled to a second transmission medium (such as copper cable) which does not require this continuous connection. This second PHY may be, for example, a G/MII device, which includes the PCS internally. The network interface card further includes a link switching unit, a physical layer interface unit, and a control unit. The control unit generates a select signal indicating which physical layer device is currently selected. Accordingly, the link switching unit transfers data between the physical layer interface unit and the currently selected physical layer device. The physical layer interface unit receives incoming data from either the link switching unit or an external interface of the network interface card. The physical layer interface unit includes two sub-layers corresponding to each of the physical devices. These sub-layers each produce outgoing data in response to the incoming data, and the appropriate outgoing data is chosen based on the currently selected physical layer device.