KS8995XA Micrel Inc, KS8995XA Datasheet - Page 23

• Manufacturer Part Number: KS8995XA
• Description: IC SWITCH 10/100 5PORT 128PQFP
• Manufacturer: Micrel Inc

Specifications of KS8995XA

• 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 Temperature Classification: Commercial
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: 576-1604 - EVAL KIT EXPERIMENTAL KS8995XA
• Lead Free Status / RoHS Status: Not Compliant, Lead free / RoHS Compliant

September 2008
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 back-off 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 10BASE-T or 100BASE-TX 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 KS8995XA 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 KS8995XA 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:
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•
•
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.) = 0x4
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