LAN9730 Datasheet, PDF (64/222 Pages) SMSC Corporation – High-Speed Inter-Chip (HSIC) USB 2.0

LAN9730/LAN9730i
4.5.3 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 device’s 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 4-45, "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. Refer to Section 6.4.1, "MAC Control Register (MAC_CR)" 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 4-45: 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 mul-
ticast addresses.
Inverse Filtering
Promiscuous
Pass all multicast frames. Frames
with physical addresses are per-
fect-filtered.
Pass all multicast frames. Frames
with physical addresses are hash-
filtered.
4.5.4 FILTERING MODES
4.5.4.1 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.
4.5.4.2 Hash Only Filtering Mode
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.
DS00001946A-page 64
 2012-2015 Microchip Technology Inc.