KS8997 Micrel Inc, KS8997 Datasheet - Page 18

• Manufacturer Part Number: KS8997
• Description: IC SWITCH 10/100 8PORT 128PQFP
• Manufacturer: Micrel Inc

Specifications of KS8997

• Applications: *
• Mounting Type: Surface Mount
• Package / Case: 128-MQFP, 128-PQFP
• Fiber Support: No
• Integrated Led Drivers: Yes
• Phy/transceiver Interface: MII
• 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: Contains lead / RoHS non-compliant

Micrel, Inc.
KS8997/KSZ8997
MAC (Media Access Controller) Operation
The KS8995X strictly abides by IEEE 802.3 standards to maximize compatibility.
Inter-Packet Gap (IPG)
If a frame is successfully transmitted, the 96 bit time IPG is measured between the two consecutive MTXEN. If the
current packet is experiencing collision, the 96 bit time IPG is measured from MCRS and the next MTXEN.
Backoff Algorithm
The KS8997 implements the IEEE Std 802.3 binary exponential back-off algorithm, and optional “aggressive mode”
back off. After 16 collisions, the packet will be optionally dropped depending on the chip configuration in Register 3.
See “Register 3.”
Late Collision
If a transmit packet experiences collisions after 512-bit times of the transmission, the packet will be dropped.
Illegal Frames
The KS8997 discards frames less than 64 bytes and can be programmed to accept frames up to 1536 bytes. Since
the KS8997 supports VLAN tags, the maximum sizing is adjusted when these tags are present.
Flow Control
The KS8997 supports standard 802.3x flow control frames on both transmit and receive sides. On the receive side, if
the KS8997 receives a pause control frame, the KS8997 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 KS8997 will be transmitted. On the transmit side, the KS8997 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 KS8997 will flow control a port, which just received a packet, if the destination port resource is being used up.
The KS8997 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 KS8997 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 flow
control mechanism from being activated and deactivated too many times. The KS8997 will flow control all ports if the
receive queue becomes full.
Half-Duplex Back Pressure
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 KS8997 will send
preambles to defer 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 free up. 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.
Broadcast Storm Protection
The KS8997 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 will use too many switch resources
(bandwidth and available space in transmit queues). The KS8997 will discard broadcast packets if the number of
those packets exceeds the threshold (configured by strapping during reset and EEPROM settings) in a preset period
of time. If the preset period expires it will then resume receiving broadcast packets until the threshold is reached. The
options are 5% of network line rate for the maximum broadcast receiving threshold or unlimited (feature off).
18
February 2007
M9999-022807-1.1