SMSC LAN9420 - Manual (Page 55)

Single-Chip Ethernet Controller with HP Auto-MDIX Support and PCI Interface
Datasheet
SMSC LAN9420/LAN9420i 55 Revision 1.22 (09-25-08)
DATASHEET
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3.5.3 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 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 3.13, "Address
Filtering Modes" , which shows the various filtering modes used by the MAC. These bits are defined in
more detail in Section 4.4.1, "MAC Control Register (MAC_CR)," on page 119 .
If the frame fails the filter, the MAC does not receive the packet. The Host has the option of accepting
or ignoring the packet.
Figure 3.18 VLAN Frame
Table 3.13 Address Filtering Modes
MCPAS PRMS INVFILT HFILT 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
PREAMBLE
(7 BYTES)
SOF
(1 BYTE)
DEST. ADDR.
(6 BYTES)
SOURCE ADDR.
(6 BYTES)
TYPE
(2 BYTES)
DATA
(46 - 1500 BYTES)
FCS
(4 BYTES)
Ethernet frame
(1518 BYTES)
PREAMBLE
(7 BYTES)
SOF
(1 BYTE)
DEST. ADDR.
(6 BYTES)
SOURCE ADDR.
(6 BYTES)
TYPE
(2 BYTES)
DATA
(46 - 1500 BYTES)
FCS
(4 BYTES)
Ethernet frame with VLAN TAG
(1522 BYTES)
TPID
(2 BYTES)
TYPE
(2 BYTES)
TPID
(2 BYTES)
USER PRIORITY
(3 BITS)
CFI
(1 BIT)
VLAN ID
(12 BITS)
Tag Control Information
(TCI)
Tag Protocol D: \x81-00
Indicates frame's priority
Canonical Address Format Indicator
VID: 12 bits defining the VLAN
to which the frame belongs