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LAN9218-MT-E2 Datasheet(PDF) 24 Page - SMSC Corporation |
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LAN9218-MT-E2 Datasheet(HTML) 24 Page - SMSC Corporation |
24 / 130 page High-Performance Single-Chip 10/100 Ethernet Controller with HP Auto-MDIX Datasheet Revision 1.5 (07-18-06) 24 SMSC LAN9218 DATASHEET 3.4 Filtering Modes 3.4.1 Perfect Filtering This filtering mode passes only incoming frames whose destination address field exactly matches the value programmed into the MAC Address High register and the MAC address low register. The MAC address is formed by the concatenation of the above two registers in the MAC CSR Function. 3.4.2 Hash Only Filtering This type of filtering checks for incoming Receive packets with either multicast or physical destination addresses, and executes an imperfect address filtering against the hash table. During imperfect hash filtering, the destination address in the incoming frame is passed through the CRC logic and the upper six bits of the CRC register are used to index the contents of the hash table. The hash table is formed by merging the register’s multicast hash table high and multicast hash table low in the MAC CSR Function to form a 64-bit hash table. The most significant bit determines the register to be used (High/Low), while the other five bits determine the bit within the register. A value of 00000 selects Bit 0 of the multicast hash table low register and a value of 11111 selects Bit 31 of the multicast hash table high register. 3.4.2.1 Hash Perfect Filtering In hash perfect filtering, if the received frame is a physical address, the LAN9218 Packet Filter block perfect-filters the incoming frame’s destination field with the value programmed into the MAC Address High register and the MAC Address Low register. If the incoming frame is a multicast frame, however, the LAN9218 packet filter function performs an imperfect address filtering against the hash table. The imperfect filtering against the hash table is the same imperfect filtering process described in the “Hash Only Filtering” section above. 3.4.2.2 Inverse Filtering In inverse filtering, the Packet Filter Block accepts incoming frames with a destination address not matching the perfect address (i.e., the value programmed into the MAC Address High register and the MAC Address Low register in the CRC block and rejects frames with destination addresses matching the perfect address. For all filtering modes, when MCPAS is set, all multicast frames are accepted. When the PRMS bit is set, all frames are accepted regardless of their destination address. This includes all broadcast frames as well. 0 0 0 1 1 Hash Filtering for physical and multicast addresses 0 0 1 0 0 Inverse Filtering X 1 0 X X Promiscuous 1 0 0 0 X Pass all multicast frames. Frames with physical addresses are perfect-filtered 1 0 0 1 1 Pass all multicast frames. Frames with physical addresses are hash- filtered Table 3.1 Address Filtering Modes (continued) MCPAS PRMS INVFILT HO HPFILT DESCRIPTION |
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