KS8997 Micrel Inc, KS8997 Datasheet - Page 17

• 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

Functional Overview: Switch Core
Address Look-Up
The internal look-up table stores MAC addresses and their associated information. It contains 1K full CAM with 48-bit
address plus switching information. The KS8997 is guaranteed to learn 1K addresses and distinguishes itself from
hash-based lookup tables which, depending on the operating environment and probabilities, may not guarantee the
absolute number of addresses it can learn.
Learning
The internal look-up engine will update its table with a new entry if the following conditions are met:
• The received packet’s SA (Source Address) does not exist in the look-up table.
• The received packet is good; the packet has no receiving errors, and is of legal length.
The look-up engine will insert the qualified SA into the table, along with the port number, time stamp. If the table is
full, the last entry of the table will be deleted first to make room for the new entry.
Migration
The internal look-up engine also monitors whether a station is moved. If it happens, it will update the table
accordingly. Migration happens when the following conditions are met:
• The received packet’s SA is in the table but the associated source port information is different.
• The received packet is good; the packet has no receiving errors, and is of legal length.
The look-up engine will update the existing record in the table with the new source port information.
Aging
The look-up engine will update time stamp information of a record whenever the corresponding SA appears. The
time stamp is used in the aging process. If a record is not updated for a period of time, the look-up engine will then
remove the record from the table. The look-up engine constantly performs the aging process and will continuously
remove aging records. The aging period is 300 seconds. This feature can be enabled or disabled by external pull-up
or pull-down resistors.
Forwarding
The KS8997 will forward packets as follows:
• If the DA look-up result is a “match”, the KS8997 will use the destination port information to determine where the
• If the DA look-up result is a “miss”, the KS8997 will forward the packet to all other ports except the port that
• All the multicast and broadcast packets will be forwarded to all other ports except the source port.
The KS8997 will not forward the following packets:
• Error packets. These include framing errors, FCS errors, alignment errors, and illegal size packet errors.
• 802.3x pause frames. The KS8997 will intercept these packets and do the appropriate actions.
• “Local” packets. Based on destination address (DA) look-up. If the destination port from the look-up table matches
Switching Engine
The KS8997 has a very high performance switching engine to move data to and from the MAC’s, packet buffers. It
operates in store and forward mode, while the efficient switching mechanism reduces overall latency.
The KS8997 has an internal buffer for frames that is 32Kx32 (128KB). This resource could be shared between the
nine ports and is programmed at system reset time by using the unmanaged program mode (I/O strapping).
Each buffer is sized at 128B and therefore there are a total of 1024 buffers available. The buffers are adaptively
allocated up to 512 to a single port based on loading.
February 2007
packet goes.
received the packet.
the port where the packet was from, the packet is defined as “local”.
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