LAN9220 datasheet(18/142 Pages) MICROCHIP

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LAN9220

DS00002417A-page 18

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3.4

Filtering Modes

3.4.1

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.

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 LAN9220 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 LAN9220 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 the “Hash Only Filter-

ing” 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 the MCPAS bit 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.

3.5

Wake-up Frame Detection

Setting the Wake-Up Frame Enable bit (WUEN) in the “WUCSR—Wake-up Control and Status Register”, places the

LAN9220 MAC in the wake-up frame detection mode. In this mode, normal data reception is disabled, and detection

logic within the MAC examines receive data for the pre-programmed wake-up frame patterns. The LAN9220 can be pro-

grammed to notify the host of the wake-up frame detection with the assertion of the host interrupt (IRQ) or assertion of

the power management event signal (PME). Upon detection, the Wake-Up Frame Received bit (WUFR) in the WUCSR

is set. When the host clears the WUEN bit the LAN9220 will resume normal receive operation.

Before putting the MAC into the wake-up frame detection state, the host must provide the detection logic with a list of

sample frames and their corresponding byte masks. This information is written into the Wake-up Frame Filter register

(WUFF). Please refer to Section 5.4.11, "WUFF—Wake-up Frame Filter," on page 102 for additional information on this

Promiscuous

Pass all multicast frames. Frames

with physical addresses are

perfect-filtered

Pass all multicast frames. Frames

with physical addresses are hash-

filtered

TABLE 3-1:

ADDRESS FILTERING MODES (CONTINUED)

MCPAS

PRMS

INVFILT

HPFILT

Description

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