LAN8740 datasheet(43/136 Pages) MICROCHIP

43 / 136 page

 2013-2015 Microchip Technology Inc.

DS00001987A-page 43

LAN8740A/LAN8740Ai

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

CRC[6] = F1 ^ F3

CRC[5] = F2 ^ F4

CRC[4] = F3 ^ F5

CRC[3] = F4 ^ F6

CRC[2] = F5 ^ F7

CRC[1] = F6

CRC[0] = F7

Determine the offset pattern with offset 0 being the first byte of the destination address. Update the offset in the

Filter Pattern Offset field of the Wakeup Filter Configuration Register A (WUF_CFGA).

Determine Address Matching Conditions:

Determine the address matching scheme based on Table 3-8 and update the Filter Broadcast Enable, Filter Any

Multicast Enable, and Address Match Enable bits of the Wakeup Filter Configuration Register A (WUF_CFGA)

accordingly.

If necessary (see step 4), set the desired MAC address to cause the wake event in the MAC Receive Address A

(RX_ADDRC).

Set the Filter Enable bit of the Wakeup Filter Configuration Register A (WUF_CFGA) to enable the filter.

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