LAN9250 datasheet(148/421 Pages) MICROCHIP

148 / 421 page

LAN9250

DS00001913A-page 148

 2015 Microchip Technology Inc.

The Filter i CRC-16 register contains the CRC-16 result of the frame that should pass Filter i.

TABLE 11-6: describes the Filter i CRC-16 bit fields.

The 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-16 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

TABLE 11-5:

FILTER I OFFSET BIT DEFINITIONS

Filter i Offset Description

Bits

Description

7:0

Pattern Offset:

The offset of the first byte in the frame on which CRC is checked for Wakeup Frame

recognition. The MAC checks the first offset byte of the frame for CRC and checks to determine

whether the frame is a Wakeup Frame. Offset 0 is the first byte of the incoming frame's destination

address.

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