KSZ8995M Micrel Inc, KSZ8995M Datasheet - Page 26

• Manufacturer Part Number: KSZ8995M
• Description: IC SWITCH 10/100 5PORT 128PQFP
• Manufacturer: Micrel Inc

Specifications of KSZ8995M

• Applications: *
• Mounting Type: Surface Mount
• Package / Case: 128-MQFP, 128-PQFP
• Number Of Primary Switch Ports: 5
• Internal Memory Buffer Size: 64
• Operating Supply Voltage (typ): 1.8/2.5/3.3V
• Fiber Support: Yes
• Integrated Led Drivers: Yes
• Phy/transceiver Interface: MII/SNI
• Power Supply Type: Analog/Digital
• Package Type: PQFP
• Data Rate (typ): 10/100Mbps
• Vlan Support: Yes
• Operating Temperature (max): 70C
• Operating Temperature (min): 0C
• Pin Count: 128
• Mounting: Surface Mount
• Jtag Support: No
• Operating Supply Voltage (max): 1.9/2.6/3.6V
• Operating Supply Voltage (min): 1.7/2.4/3V
• Operating Temperature Classification: Commercial
• Data Rate: 100Mbps
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 576-1607 - BOARD EVAL EXPERIMENT KSZ8995MA
• Lead Free Status / RoHS Status: Compliant, Lead free / RoHS Compliant
• Other names: 576-1038

KS8995M
Late Collision
If a transmit packet experiences collisions after 512-bit times of the transmission, the packet will be dropped.
Illegal Frames
The KS8995M discards frames less than 64 bytes and can be programmed to accept frames up to 1536 bytes in register 4.
For special applications, the KS8995M can also be programmed to accept frames up to 1916 bytes in register 4. Since the
KS8995M supports VLAN tags, the maximum sizing is adjusted when these tags are present.
Flow Control
The KS8995M supports standard 802.3x flow control frames on both transmit and receive sides.
On the receive side, if the KS8995M receives a pause control frame, the KS8995M will not transmit the next normal frame until
the timer, specified in the pause control frame, expires. If another pause frame is received before the current timer expires,
the timer will be updated with the new value in the second pause frame. During this period (being flow controlled), only flow
control packets from the KS8995M will be transmitted.
On the transmit side, the KS8995M has intelligent and efficient ways to determine when to invoke flow control. The flow control
is based on availability of the system resources, including available buffers, available transmit queues and available receive
queues.
The KS8995M will flow control a port, which just received a packet, if the destination port resource is being used up. The
KS8995M will issue a flow control frame (XOFF), containing the maximum pause time defined in IEEE standard 802.3x. Once
the resource is freed up, the KS8995M will send out the other flow control frame (XON) with zero pause time to turn off the
flow control (turn on transmission to the port). A hysteresis feature is provided to prevent the flow control mechanism from being
activated and deactivated too many times.
The KS8995M will flow control all ports if the receive queue becomes full.
Half-Duplex Back Pressure
A half-duplex back pressure option (note: not in 802.3 standards) is also provided. The activation and deactivation conditions
are the same as the above in full-duplex mode. If back pressure is required, the KS8995M will send preambles to defer the
other stations’ transmission (carrier sense deference). To avoid jabber and excessive deference defined in 802.3 standard,
after a certain time it will discontinue the carrier sense but it will raise the carrier sense quickly. This short silent time (no carrier
sense) is to prevent other stations from sending out packets and keeps other stations in carrier sense deferred state. If the port
has packets to send during a back pressure situation, the carrier-sense-type back pressure will be interrupted and those
packets will be transmitted instead. If there are no more packets to send, carrier-sense-type back pressure will be active again
until switch resources are free. If a collision occurs, the binary exponential backoff algorithm is skipped and carrier sense is
generated immediately, reducing the chance of further colliding and maintaining carrier sense to prevent reception of packets.
To ensure no packet loss in 10BaseT or 100BaseTX half-duplex modes, the user must enable the following:
These bits are not set as the default because this is not the IEEE standard.
Broadcast Storm Protection
The KS8995M has an intelligent option to protect the switch system from receiving too many broadcast packets. Broadcast
packets will be forwarded to all ports except the source port, and thus use too many switch resources (bandwidth and available
space in transmit queues). The KS8995M 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 50ms
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 and
Register 7. The default setting for registers 6 and 7 is 0x4A, which is 74 decimal. This is equal to a rate of 1%, calculated as
follows:
MII Interface Operation
The MII (Media Independent Interface) is specified by the IEEE 802.3 committee and provides a common interface between
physical layer and MAC layer devices. The KS8995M provides two such interfaces. The MII-P5 interface is used to connect
to the fifth PHY, whereas the MII-SW interface is used to connect to the fifth MAC. Each of these MII interfaces contains two
distinct groups of signals, one for transmission and the other for receiving. Table 5 describes the signals used in the MII-P5
interface.
M9999-120403
• Aggressive backoff (register 3, bit 0)
• No excessive collision drop (register 4, bit 3)
• Back pressure (register 4, bit 5)
148,800 frames/sec
50ms/interval
1% = 74 frames/interval (approx.) = 0x4A
26
December 2003
Micrel