LAN9220 datasheet(19/142 Pages) MICROCHIP

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DS00002417A-page 19

LAN9220

The MAC supports four programmable filters that support many different receive packet patterns. If remote wake-up

mode is enabled, the remote wake-up function receives all frames addressed to the MAC. It then checks each frame

against the enabled filter and recognizes the frame as a remote wake-up frame if it passes the wakeup frame filter reg-

ister’s address filtering and CRC value match.

In order to determine which bytes of the frames should be checked by the CRC module, the MAC uses a programmable

byte mask and a programmable pattern offset for each of the four supported filters.

The pattern’s offset defines the location of the first byte that should be checked in the frame. Since the destination

address is checked by the address filtering Function, the pattern offset is always greater than 12.

The byte mask is a 31-bit field that specifies whether or not each of the 31 contiguous bytes within the frame, beginning

in the pattern offset, should be checked. If bit j in the byte mask is set, the detection logic checks byte offset +j in the

frame. In order to load the Wake-up Frame Filter register, the host LAN driver software must perform eight writes to the

Wake-up Frame Filter register (WUFF). The Diagram shown in Table 3-2, "Wake-Up Frame Filter Register Structure"

below, shows the wake-up frame filter register’s structure.

Note 3-1

Wake-up frame detection can be performed when the LAN9220 is in the D0 or D1 power states. In

the D0 state, wake-up frame detection is enabled when the WUEN bit is set.

Note 3-2

Wake-up frame detection, as well as Magic Packet detection, is always enabled and cannot be

disabled when the device enters the D1 state.

Note 3-3

When wake-up frame detection is enabled via the WUEN bit of the WUCSR—Wake-up Control and

Status Register, a broadcast wake-up frame will wake-up the device despite the state of the Disable

Broadcast Frame (BCAST) bit in the MAC_CR—MAC Control Register.

The Filter i Byte Mask defines which incoming frame bytes Filter i will examine to determine whether or not this is a

wake-up frame. Table 3-3, describes the byte mask’s bit fields.

The Filter i command register controls Filter i operation. Table 3-4 shows the Filter I command register.

TABLE 3-2:

WAKE-UP FRAME FILTER REGISTER STRUCTURE

Filter 0 Byte Mask

Filter 1 Byte Mask

Filter 2 Byte Mask

Filter 3 Byte Mask

Reserved

Filter 3

Command

Reserved

Filter 2

Command

Reserved

Filter 1

Command

Reserved

Filter 0

Command

Filter 3 Offset

Filter 2 Offset

Filter 1Offset

Filter 0 Offset

Filter 1 CRC-16

Filter 0 CRC-16

Filter 3 CRC-16

Filter 2 CRC-16

TABLE 3-3:

FILTER I BYTE MASK BIT DEFINITIONS

Filter i Byte Mask Description

Field

Description

Must be zero (0)

30:0

Byte Mask: If bit j of the byte mask is set, the CRC machine processes byte number pattern - (offset

+ j) of the incoming frame. Otherwise, byte pattern - (offset + j) is ignored.

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