Datasheet

Micrel, Inc.
KSZ8081MNX/KSZ8081RNB
August
19, 2015 22
Revision 1.4
MII Interface (KSZ8081MNX Only)
The Media Independent Interface (MII) is compliant with the IEEE 802.3 Specification. It provides a common interface
between MII PHYs and MACs, and has the following key characteristics:
• Pin count is 15 pins (6 pins for data transmission, 7 pins for data reception, and 2 pins for carrier and collision
indication).
• 10Mbps and 100Mbps data rates are supported at both half- and full-duplex.
• Data transmission and reception are independent and belong to separate signal groups.
• Transmit data and receive data are each 4 bits wide, a nibble.
By default, the KSZ8081MNX is configured to MII mode after it is powered up or hardware reset with the following:
• A 25MHz crystal connected to XI, XO (pins 9, 8), or an external 25MHz clock source (oscillator) connected to XI.
• The CONFIG[2:0] strapping pins (pins 18, 29, 28) set to 000 (default setting).
MII Signal Definition
Table 1 describes the MII signals. Refer to Clause 22 of the IEEE 802.3 Specification for detailed information.
Table 1. MII Signal Definition
MII Signal Name
Direction
(with respect to PHY,
KSZ8081MNX signal)
Direction
(with respect to MAC)
Description
TXC Output Input
Transmit Clock
(2.5MHz for 10Mbps; 25MHz for 100Mbps)
TXEN Input Output Transmit Enable
TXD[3:0] Input Output Transmit Data[3:0]
RXC Output Input
Receive Clock
(2.5MHz for 10Mbps; 25MHz for 100Mbps)
RXDV Output Input Receive Data Valid
RXD[3:0] Output Input Receive Data[3:0]
RXER Output Input, or (not required) Receive Error
CRS Output Input Carrier Sense
COL Output Input Collision Detection
Transmit Clock (TXC)
TXC is sourced by the PHY. It is a continuous clock that provides the timing reference for TXEN and TXD[3:0]. TXC is
2.5MHz for 10Mbps operation and 25MHz for 100Mbps operation.
Transmit Enable (TXEN)
TXEN indicates that the MAC is presenting nibbles on TXD[3:0] for transmission. It is asserted synchronously with the first
nibble of the preamble and remains asserted while all nibbles to be transmitted are presented on the MII. It is negated
before the first TXC following the final nibble of a frame.
TXEN transitions synchronously with respect to TXC.