MII（media-independent interface）提供了MAC（media access control）與PHY（Ethernet physical layer）之間的互聯技術，該介面支持10Mb/s與100Mb/s的數據傳輸速率，數據傳輸的位寬為4位。MDIO（Management... ...
MII（media-independent interface）提供了MAC（media access control）與PHY（Ethernet physical layer）之間的互聯技術，該介面支持10Mb/s與100Mb/s的數據傳輸速率，數據傳輸的位寬為4位。MDIO（Management Data Input/Output）是一個兩線串列管理匯流排，可掛載32個設備，MII中使用它實現對PHY的管理。
MII
以前的10M的MAC層晶元和物理層晶元之間傳送數據是通過一根數據線來進行的，其時鐘是10M。在100M中，如果也用一根數據線來傳送的話，時鐘需要100M，這會帶來一些問題，所以定義了MII介面，它是用4根數據線來傳送數據的，這樣在傳送100M數據時，時鐘就會由100M降低為25M，而在傳送10M數據時，時鐘會降低到2.5M，這樣就實現了10M和100M的相容。
MII介面主要包括四個部分。一是從MAC層到物理層的發送數據介面，二是從物理層到MAC層的接收數據介面，三是從物理層到MAC層的狀態指示信號，四是MAC層和物理層之間傳送控制和狀態信息的MDIO介面,共18根信號線。如下圖所示,除MDIO以外（未畫出控制信號）的典型數據信號介面圖：
| Signal | Description |
|---|---|
| TXD0~3 | Transmit Data. parallel data signals that are driven by the MAC |
| TX_EN | Transmit Enable. The MAC asserts this signal when it drives valid data on TXD |
| TX_CLK | Transmit Clock. TX_CLK is sourced by the PHY in both 10 and 100 Mbps operations.2.5 MHz for 10 Mbps operation, 25 MHz for 100 Mbps operation. |
| RXD0~3 | Receive Data. RXD is a bundle of parallel signals that transition synchronously with respect to the RX_CLK |
| RX_DV | Receive Data Valid. The PHY asserts this signal when it drives valid data on RXD |
| RX_ER | Receive Error. Signals a receive error condition has occurred |
| TX_ER | Transmit Error. Signals a transmit error condition |
| RX_CLK | Receive Clock. 25 MHz for 100 Mbps operation, 2.5 MHz for10 Mbps operation |
| COL | Collision Detected. The PHY asserts this output when acollision is detected |
| CRS | Carrier Sense. During half-duplex(半雙工）operation,the PHY asserts this output when either transmitting or receiving data packets. During full-duplex operation , CRS is asserted only during receive |
MDIO
MDIO屬MII的管理介面。有兩根線（MDIO for data, MDC for clock)。主要用來實現MAC對PHY的控制管理。
讀時序
寫時序
幀格式
| R/W | PRE | ST | OP | PHYAD | REGAD | TA | DATA | IDLE |
|---|---|---|---|---|---|---|---|---|
| READ | 1...1 | 01 | 10 | AAAAA | RRRRR | Z0 | DDDDDDDDDDDDDDDD | Z |
| WRITE | 1...1 | 01 | 01 | AAAAA | RRRRR | 10 | DDDDDDDDDDDDDDDD | Z |
References
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