LAN9117_08 Datasheet, PDF (27/136 Pages) SMSC Corporation – High Performance Single-Chip 10/100 Non-PCI Ethernet Controller

High Performance Single-Chip 10/100 Non-PCI Ethernet Controller
Datasheet
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 Control Register”. Please refer to Section 5.4.1,
"MAC_CR—MAC Control Register," on page 99 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.
Table 3.1 Address Filtering Modes
MCPAS
PRMS
INVFILT
HO
0
0
0
0
0
0
0
0
0
0
0
1
0
0
1
0
X
1
0
X
1
0
0
0
1
0
0
1
HPFILT
0
1
1
0
X
X
1
DESCRIPTION
MAC address perfect filtering only
for all addresses.
MAC address perfect filtering for
physical address and hash filtering
for multicast addresses
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
3.4.1
3.4.2
Filtering Modes
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.
SMSC LAN9117
27
DATASHEET
Revision 1.5 (07-11-08)