LAN9220 Datasheet, PDF (25/150 Pages) SMSC Corporation – 16-bit Non-PCI Small Form Factor 10/100 Ethernet Controller with Variable Voltage I/O & HP Auto-MDIX Support

16-bit Non-PCI Small Form Factor 10/100 Ethernet Controller with Variable Voltage I/O & HP Auto-MDIX Support
Datasheet
Table 3.1 Address Filtering Modes (continued)
MCPAS
PRMS
INVFILT
HO
0
0
0
1
0
0
1
0
X
1
0
X
1
0
0
0
1
0
0
1
HPFILT
1
0
X
X
1
DESCRIPTION
Hash Filtering for physical and
multicast addresses
Inverse Filtering
Promiscuous
Pass all multicast frames. Frames
with physical addresses are
perfect-filtered
Pass all multicast frames. Frames
with physical addresses are hash-
filtered
3.4
Filtering Modes
3.4.1
3.4.2
3.4.2.1
3.4.2.2
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.
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.
Hash Perfect Filtering
In hash perfect filtering, if the received frame is a physical address, the LAN9220 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 LAN9220 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.
Inverse Filtering
In inverse filtering, thePacket 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 the MCPAS bit 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.
SMSC LAN9220
25
DATASHEET
Revision 2.6 (12-04-08)