KSZ8893-MQL Micrel Semiconductor, Inc., KSZ8893-MQL Datasheet - Page 32

• Manufacturer Part Number: KSZ8893-MQL
• Description: Integrated 3-Port 10/100 Managed Switch with PHYs
• Manufacturer: Micrel Semiconductor, Inc.

type backpressure is reactivated again until switch resources free up. If a collision occurs, the binary exponential
back-off algorithm is skipped and carrier sense is generated immediately, thus reducing the chance of further
collisions and carrier sense is maintained to prevent packet reception.
To ensure no packet loss in 10 BASE-T or 100 BASE-TX half duplex modes, the user must enable the following:
1. Aggressive back-off (register 3 (0x03), bit [0])
2. No excessive collision drop (register 4 (0x04), bit [3])
Note: These bits are not set as defaults, as this is not the IEEE standard.
Broadcast Storm Protection
The KSZ8893MQL has an intelligent option to protect the switch system from receiving too many broadcast
packets. As the broadcast packets are forwarded to all ports except the source port, an excessive number of
switch resources (bandwidth and available space in transmit queues) may be utilized. The KSZ8893MQL has the
option to include “multicast packets” for storm control. The broadcast storm rate parameters are programmed
globally, and can be enabled or disabled on a per port basis. The rate is based on a 67ms interval for 100BT and
a 500ms interval for 10BT. At the beginning of each interval, the counter is cleared to zero, and the rate limit
mechanism starts to count the number of bytes during the interval. The rate definition is described in register 6
(0x06) and 7 (0x07). The default setting is 0x63 (99 decimal). This is equal to a rate of 1%, calculated as follows:
Note: 148,800 frames/sec is based on 64-byte block of packets in 100BASE-TX with 12 bytes of IPG and 8 bytes
of preamble between two packets.
MII Interface Operation
The Media Independent Interface (MII) is specified in Clause 22 of the IEEE 802.3u Standard. It provides a
common interface between physical layer and MAC layer devices. The MII provided by the KSZ8893MQL is
connected to the device’s third MAC. The interface contains two distinct groups of signals: one for transmission
and the other for reception. The following table describes the signals used by the MII bus.
Micrel
November 2005
External MAC
Controller Signals
MTXEN
MTXER
MTXD3
MTXD2
MTXD1
MTXD0
MTXC
MCOL
MCRS
MRXDV
MRXER
MRXD3
MRXD2
MRXD1
MRXD0
MRXC
PHY-Mode Connections
148,800 frames/sec * 67ms/interval * 1% = 99 frames/interval (approx.) = 0x63
KSZ8893MQL
PHY Signals
SMTXEN
SMTXER
SMTXD[3]
SMTXD[2]
SMTXD[1]
SMTXD[0]
SMTXC
SCOL
SCRS
SMRXDV
(not used)
SMRXD[3]
SMRXD[2]
SMRXD[1]
SMRXD[0]
SMRXC
Pin
Descriptions
Transmit enable
Transmit error
Transmit data bit 3
Transmit data bit 2
Transmit data bit 1
Transmit data bit 0
Transmit clock
Collision detection
Carrier sense
Receive data valid
Receive error
Receive data bit 3
Receive data bit 2
Receive data bit 1
Receive data bit 0
Receive clock
Table 3. MII Signals
32
MAC-Mode Connections
External
PHY Signals
MTXEN
MTXER
MTXD3
MTXD2
MTXD1
MTXD0
MTXC
MCOL
MCRS
MRXDV
MRXER
MRXD3
MRXD2
MRXD1
MRXD0
MRXC
KSZ8893MQL
MAC Signals
SMRXDV
(not used)
SMRXD[3]
SMRXD[2]
SMRXD[1]
SMRXD[0]
SMRXC
SCOL
SCRS
SMTXEN
SMTXER
SMTXD[3]
SMTXD[2]
SMTXD[1]
SMTXD[0]
SMTXC
KSZ8893MQL/MQLI
M9999-111705