KS8995E Micrel Inc, KS8995E Datasheet - Page 19

• Manufacturer Part Number: KS8995E
• Manufacturer: Micrel Inc

Specifications of KS8995E

• Number Of Primary Switch Ports: 5
• 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: Not 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 KS8995E is guaranteed to learn 1K addresses and distinguishes itself from hash-based look-
up 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 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 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 KS8995E will forward packets as follows:
The KS8995E will not forward the following packets:
Switching Engine
The KS8995E 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 KS8995E has in internal buffer for frames that is 32Kx32 (128KB). This resource is shared between the five ports. Buffer
sizing per port can be 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. A per port maximum can be set at 205
(equal allocation), 512 or 768. There is also an adaptive 512 size mode that reacts to port traffic.
MAC (Media Access Controller) Operation
The KS8995E strictly abides by IEEE 802.3 standard 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 KS8995E 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.
August 2003
KS8995E
• The received packet’s SA 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 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.
• If the DA look-up results is a “match”, the KS8995E will use the destination port information to determine where the
• If the DA look-up result is a “miss”, the KS8995E will forward the packet to all other ports except the port that received
• All the multicast and broadcast packets will be forwarded to all other ports except the source port.
• Error packets. These include framing errors, FCS errors, alignment errors, and illegal size packet errors.
• 802.3x pause frames. The KS8995E 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
packet goes.
the packet.
the port where the packet was from, the packet is defined as “local”.
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KS8995E
Micrel