LAN9250 datasheet(142/421 Pages) MICROCHIP

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LAN9250

DS00001913A-page 142

 2015 Microchip Technology Inc.

11.4

Address Filtering

The Ethernet address fields of an Ethernet packet consist 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 Host MAC address check logic filters the frame based on the Ethernet receive filter mode that has been enabled.

The various filter modes of the Host MAC are specified based on the state of the control bits in the Host MAC Control

(HMAC_CR)," on page 193 for more information on this register.

Frames that fail the address filtering are accepted only if the Receive All Mode (RXALL) bit in the Receive Configuration

11.4.1

PERFECT FILTERING

This filtering mode passes only incoming frames whose destination address field exactly matches the value pro-

grammed into the Host MAC Address High Register (HMAC_ADDRH) and the Host MAC Address Low Register

(HMAC_ADDRL). The MAC address is formed by the concatenation of these two registers.

Broadcast frames are also accepted if Disable Broadcast Frames (BCAST) is low.

Note:

If the HMAC_ADDRH and HMAC_ADDRL registers are set to the Broadcast address, Broadcast frames will

be accepted regardless of the setting of the BCAST bit.

TABLE 11-1:

ADDRESS FILTERING MODES

MCPAS

PRMS

INVFILT

HPFILT

Description

Perfect

- MAC address perfect fil-

tering only for all addresses.

Broadcast frames accepted if

BCAST is low.

Hash Perfect

- MAC address per-

fect filtering for physical address

and hash filtering for multicast

addresses. Broadcast frames

accepted if BCAST is low.

Hash Only

- Hash Filtering for

physical and multicast addresses.

Broadcast frames accepted if

BCAST is low.

Inverse Filtering

Promiscuous

Perfect all Multicast

- Pass all

multicast frames including broad-

casts. Frames with physical

addresses are perfect-filtered

Hash Only all Multicast

- Pass all

multicast frames including broad-

casts. Frames with physical

addresses are hash-filtered

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