Datasheet

LAN8740A/LAN8740Ai
DS00001987A-page 26  2013-2015 Microchip Technology Inc.
3.4 MAC Interface
The MII/RMII block is responsible for communication with the MAC controller. Special sets of hand-shake signals are
used to indicate that valid received/transmitted data is present on the 4 bit receive/transmit bus.
The device must be configured in MII or RMII mode. This is done by specific pin strapping configurations. Refer to Sec-
tion 3.4.3, "MII vs. RMII Configuration" for information on pin strapping and how the pins are mapped differently.
3.4.1 MII
The MII includes 16 interface signals:
• Transmit data - TXD[3:0]
• Transmit strobe - TXEN
• Transmit clock - TXCLK
• Transmit error - TXER/TXD4
• Receive data - RXD[3:0]
• Receive strobe - RXDV
• Receive clock - RXCLK
• Receive error - RXER/RXD4/PHYAD0
• Collision indication - COL
• Carrier sense - CRS
In MII mode, on the transmit path, the transceiver drives the transmit clock, TXCLK, to the controller. The controller syn-
chronizes the transmit data to the rising edge of TXCLK. The controller drives TXEN high to indicate valid transmit data.
The controller drives TXER high when a transmit error is detected.
On the receive path, the transceiver drives both the receive data, RXD[3:0], and the RXCLK signal. The controller clocks
in the receive data on the rising edge of RXCLK when the transceiver drives RXDV high. The transceiver drives RXER
high when a receive error is detected.
3.4.2 RMII
The device supports the low pin count Reduced Media Independent Interface (RMII) intended for use between Ethernet
transceivers and switch ASICs. Under IEEE 802.3, an MII comprised of 16 pins for data and control is defined. In devices
incorporating many MACs or transceiver interfaces such as switches, the number of pins can add significant cost as the
port counts increase. RMII reduces this pin count while retaining a management interface (MDIO/MDC) that is identical
to MII.
The RMII interface has the following characteristics:
• It is capable of supporting 10 Mbps and 100 Mbps data rates
• A single clock reference is used for both transmit and receive
• It provides independent 2-bit (di-bit) wide transmit and receive data paths
• It uses LVCMOS signal levels, compatible with common digital CMOS ASIC processes
The RMII includes the following interface signals (1 optional):
• Transmit data - TXD[1:0]
• Transmit strobe - TXEN
• Receive data - RXD[1:0]
• Receive error - RXER (Optional)
• Carrier sense - CRS_DV
• Reference Clock - (RMII references usually define this signal as REF_CLK)