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전자부품 데이터시트 검색엔진 |
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LAN9117 데이터시트(HTML) 20 Page - Microchip Technology |
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LAN9117 데이터시트(HTML) 20 Page - Microchip Technology |
20 / 114 page ![]() LAN9117 DS00002267A-page 20 2005-2016 Microchip Technology Inc. 3.3 Address Filtering Functional Description The Ethernet address fields of an Ethernet Packet, consists of two 6-byte fields: one for the destination address and one for the source address. The first bit of the destination address signifies whether it is a physical address or a multicast address. The LAN9117 address check logic filters the frame based on the Ethernet receive filter mode that has been enabled. Filter modes are specified based on the state of the control bits in Table 3-1, "Address Filtering Modes", which shows the various filtering modes used by the Ethernet MAC Function. These bits are defined in more detail in the “MAC Con- trol Register”. Please refer to Section 5.4.1, "MAC_CR—MAC Control Register," on page 80 for more information on this register. If the frame fails the filter, the Ethernet MAC function does not receive the packet. The host has the option of accepting or ignoring the packet. 3.4 Filtering Modes 3.4.1 PERFECT FILTERING This filtering mode passes only incoming frames whose destination address field exactly matches the value pro- grammed 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 LAN9117 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 LAN9117 packet filter function performs an imper- fect address filtering against the hash table. The imperfect filtering against the hash table is the same imperfect filtering process described in the “Hash Only Filter- ing” section above. TABLE 3-1: ADDRESS FILTERING MODES MCPAS PRMS INVFILT HO HPFILT Description 0 0 0 0 0 MAC address perfect filtering only for all addresses. 0 0 0 0 1 MAC address perfect filtering for physical address and hash filtering for multicast addresses 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 |
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