Rockwell-automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command Manuel d'utilisateur Page 79

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5–7Data-link Layer Message Frames
Publication
17706.5.16 - October 1996
The full-duplex and half-duplex slave and master protocol examples
below provide you with procedures for determining the CRC-16
value.
Full-duplex and half-duplex slave protocol
data_byte = all linklayer data, ETX
CLEAR CRC_REGISTER
FOR each data_byte
GET data_byte
XOR (data_byte, right eight bits of CRC_REGISTER)
PLACE RESULT in right eight bits of CRC_REGISTER)
DO 8 times (on CRC register_
Shift bit right, shift in 0 at left
IF bit shifted = 1
XOR (CONSTANT, CRC_REGISTER)
PLACE RESULT in CRC_REGISTER
END IF
END DO
END FOR
TRANSMIT CRC_REGISTER as 2byte CRC field (low byte, high byte)
Half-duplex master protocol
data_byte = STN, STX, all linklayer data, ETX
CLEAR CRC_REGISTER
For each data_byte
GET data_byte
XOR (data_byte, right 8 bits of CRC_REGISTER)
PLACE RESULT in right 8 bits of CRC_REGISTER
DO 8 times
Shift bit right, shift in 0 at left
IF bit shifted = 1
XOR (CONSTANT, CRC_REGISTER)
PLACE RESULT in CRC_REGISTER
END IF
END DO
END FOR
TRANSMIT CRC_REGISTER as 2 byte CRC field
Below is an actual frame that you can use to validate your CRC
routine:
Use this frame to validate the CRC
53 B911 004110 02 07 00 00 00 00 00 00 00 00 00 00 00 00 10 03 6B 4C
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