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KSZ8873MLLJ Datasheet(PDF) 24 Page - Micrel Semiconductor |
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KSZ8873MLLJ Datasheet(HTML) 24 Page - Micrel Semiconductor |
24 / 108 page Micrel, Inc. KSZ8873MLLJ September 2011 24 M9999-091911-1.8 Hardware Power Down KSZ8873 supports a hardware power down mode. When the pin PWRDN is actived low, the entire chip is powered down. Functional Overview: MAC and Switch Address Lookup The internal lookup table stores MAC addresses and their associated information. It contains a 1K unicast address table plus switching information. The KSZ8873MLLJ 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 lookup engine updates its table with a new entry if the following conditions are met: 1. The received packet's Source Address (SA) does not exist in the lookup table. 2. The received packet is good; the packet has no receiving errors, and is of legal length. The lookup engine inserts the qualified SA into the table, along with the port number and time stamp. If the table is full, the last entry of the table is deleted to make room for the new entry. Migration The internal lookup engine also monitors whether a station has moved. If a station has moved, it will update the table accordingly. Migration happens when the following conditions are met: 1. The received packet's SA is in the table but the associated source port information is different. 2. The received packet is good; the packet has no receiving errors, and is of legal length. The lookup engine will update the existing record in the table with the new source port information. Aging The lookup engine updates the 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 lookup engine removes the record from the table. The lookup engine constantly performs the aging process and will continuously remove aging records. The aging period is about 200 seconds. This feature can be enabled or disabled through register 3 (0x03) bit [2]. Forwarding The KSZ8873MLLJ forwards packets using the algorithm that is depicted in the following flowcharts. Figure 4 shows stage one of the forwarding algorithm where the search engine looks up the VLAN ID, static table, and dynamic table for the destination address, and comes up with “port to forward 1” (PTF1). PTF1 is then further modified by spanning tree, IGMP snooping, port mirroring, and port VLAN processes to come up with “port to forward 2” (PTF2), as shown in Figure 5. The packet is sent to PTF2. |
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