Network data on the interface is framed using the IEEE Ethernet standard. On a PC the CNR connector Type B carries MII signals. The MII can be used to connect a MAC to an external PHY using a pluggable connector, or directly to a PHY chip on the same PCB. Thus any MAC may be used with any PHY, independent of the network signal transmission media. twisted pair, fiber optic, etc.) can be used without redesigning or replacing the MAC hardware. Being media independent means that different types of PHY devices for connecting to different media (i.e. The MII is standardized by IEEE 802.3u and connects different types of PHYs to MACs. The media-independent interface ( MII) was originally defined as a standard interface to connect a Fast Ethernet (i.e., 100 Mbit/s) media access control (MAC) block to a PHY chip. The expanded device type allows the STA to access other devices in addition to PHYs.Īdditional details about Clause 45 can be found on the IEEE 802.3 workgroup website.MII connector on a Sun Ultra 1 Creator workstation Since the register address is no longer needed, this field is replaced with DEVTYPE to specify the targeted device type. The OP codes were expanded to specify an address frame, a write frame, a read frame, or a read and post read increment address frame. A new ST code (00) is defined to identify Clause 45 data frames. In order to accomplish this, several changes were made in the composition of the data frame. Secondly, by creating a address frame, the register address space is increased from 5 bits to 16 bits, which allows an STA to access 65,536 different registers. The benefits of adding this two cycle access are that Clause 45 is backwards compatible with Clause 22, allowing devices to interoperate with each other. A second frame is then sent to perform the read or write. First an address frame is sent to specify the MMD and register. In Clauses 22, a single frame specified both the address and the data to read or write. The primary change in Clause 45 is how the registers are accessed. Turnaround time to change bus ownership from STA to MMD if requiredĭriven by MMD during read-increment-address Clause 22Ĭlause 22 defines the MDIO communication basic frame format (figure 13) which is composed of the following elements: MDC is specified to have a frequency of up to 2.5 MHz. The STA initiates all communication in MDIO and is responsible for driving the clock on MDC. The target devices that are being managed by the MDC are referred to as MDIO Manageable Devices (MMD). The device driving the MDIO bus is identified as the Station Management Entity (STA). ![]() MDIO has specific terminology to define the various devices on the bus. The MDIO bus has two signals: Management Data Clock (MDC) and Managment Data Input/Ouput (MDIO). ![]()
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