LAN8742AI-CZ datasheet(43/124 Pages) MICROCHIP

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DS00001989A-page 43

LAN8742A/LAN8742Ai

The pattern offset defines the location of the first byte that should be checked in the frame. The byte mask is a 128-bit

field that specifies whether or not each of the 128 contiguous bytes within the frame, beginning with the pattern offset,

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

otherwise byte (pattern offset + j) is ignored.

At the completion of the CRC-16 checking process, the CRC-16 calculated using the pattern offset and byte mask is

compared to the expected CRC-16 value associated with the filter. If a match occurs, a remote wake-up event is sig-

naled. The frame must also pass the FCS check and packet length checking.

Table 3-7 indicates the cases that produce a wake-up event. All other cases do not generate a wake-up event.

As an example, the Host system must perform the following steps to enable the device to assert nINT on detection of a

Wakeup Frame WoL event:

Declare Pattern:

Update the Wakeup Filter Byte Mask Registers (WUF_MASK) to indicate the valid bytes to match.

Calculate the CRC-16 value of valid bytes off-line and update the Wakeup Filter Configuration Register B

(WUF_CFGB). CRC-16 is calculated as follows:

At the start of a frame, CRC-16 is initialized with the value FFFFh. CRC-16 is updated when the pattern offset and mask

indicate the received byte is part of the checksum calculation. The following algorithm is used to update the CRC-16 at

that time:

Let:

^ denote the exclusive or operator.

Data [7:0] be the received data byte to be included in the checksum.

CRC[15:0] contain the calculated CRC-16 checksum.

F0 … F7 be intermediate results, calculated when a data byte is determined to be part of the CRC-16.

Calculate:

F0 = CRC[15] ^ Data[0]

F1 = CRC[14] ^ F0 ^ Data[1]

F2 = CRC[13] ^ F1 ^ Data[2]

F3 = CRC[12] ^ F2 ^ Data[3]

F4 = CRC[11] ^ F3 ^ Data[4]

F5 = CRC[10] ^ F4 ^ Data[5]

F6 = CRC[09] ^ F5 ^ Data[6]

F7 = CRC[08] ^ F6 ^ Data[7]

The CRC-32 is updated as follows:

CRC[15] = CRC[7] ^ F7

CRC[14] = CRC[6]

CRC[13] = CRC[5]

CRC[12] = CRC[4]

CRC[11] = CRC[3]

CRC[10] = CRC[2]

CRC[9] = CRC[1] ^ F0

CRC[8] = CRC[0] ^ F1

CRC[7] = F0 ^ F2

TABLE 3-7:

WAKEUP GENERATION CASES

Filter Enabled

Frame Type

CRC Matches

Address

Match

Enabled

Any MCAST

Enabled

BCAST

Enabled

Frame

Address

Matches

Yes

Unicast

Yes

Unicast

Yes

Multicast

Yes

Multicast

Yes

Broadcast

Yes

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