High-Performance Single-Chip 10/100 Ethernet Controller with HP Auto-MDIX
Datasheet
Table 3.1 Address Filtering Modes (continued)
MCPAS
PRMS
INVFILT
HO
HPFILT
DESCRIPTION
0
0
0
1
1
Hash Filtering for physical and
multicast addresses
0
X
1
0
1
0
1
0
0
0
X
0
0
X
X
Inverse Filtering
Promiscuous
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
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.
Revision 1.5 (07-18-06)
SMSC LAN9218
DATA2S4HEET
SMSC [ SMSC CORPORATION ]
