LAN9500 Datasheet, PDF(58/213 Page) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

English

English German Russian Spanish Italian Polish Chinese Japanese Korean French Portuguese	Language :

LAN9500 Datasheet, PDF (58/213 Pages) SMSC Corporation – USB 2.0 to 10/100 Ethernet Controller Promiscuous mode

◁

LAN950x

5.5.3 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 deviceâs 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 5-45, "Address Filtering Modes", which shows

the various filtering modes used by the Ethernet MAC Function. These bits are defined in more detail in the âMAC Con-

trol Registerâ. Please refer to Section 7.4.1, "MAC Control Register (MAC_CR)," on page 159 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 5-45:

MCPAS

ADDRESS FILTERING MODES

PRMS

INVFILT

HPFILT

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

5.5.4 FILTERING MODES

5.5.4.1 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.

5.5.4.2 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 registerâs 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.

5.5.4.3 Hash Perfect Filtering

In hash perfect filtering, if the received frame is a physical address, the deviceâs Packet Filter block perfect-filters the

incoming frameâs 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 deviceâs packet filter function performs an imper-

fect address filtering against the hash table.

The imperfect filtering against the hash table is the same imperfect filtering process described in Section 5.5.4.2, "Hash

Only Filtering Mode".

DS00001875A-page 58

ï£ 2010 - 2015 Microchip Technology Inc.

▷