Steps For Calculation Of Crc (Cyclical Redundancy Check) - Delta Electronics AC Motor Drive VFD-E User Manual

Chapter 4 Parameters|
01H+03H+04H+01H+00H+01H=0AH, the 2's-complement negation of 0AH is F6H.
RTU mode:
CRC (Cyclical Redundancy Check) is calculated by the following steps:
Step 1: Load a 16-bit register (called CRC register) with FFFFH.
Step 2: Exclusive OR the first 8-bit byte of the command message with the low order byte of
the 16-bit CRC register, putting the result in the CRC register.
Step 3: Examine the LSB of CRC register.
Step 4: If the LSB of CRC register is 0, shift the CRC register one bit to the right with MSB
zero filling, then repeat step 3. If the LSB of CRC register is 1, shift the CRC register one bit
to the right with MSB zero filling, Exclusive OR the CRC register with the polynomial value
A001H, then repeat step 3.
Step 5: Repeat step 3 and 4 until eight shifts have been performed. When this is done, a
complete 8-bit byte will have been processed.
Step 6: Repeat step 2 to 5 for the next 8-bit byte of the command message. Continue doing
this until all bytes have been processed. The final contents of the CRC register are the CRC
value. When transmitting the CRC value in the message, the upper and lower bytes of the
CRC value must be swapped, i.e. the lower order byte will be transmitted first.
The following is an example of CRC generation using C language. The function takes two
arguments:
Unsigned char* data
Unsigned char length
The function returns the CRC value as a type of unsigned integer.
4-122
LRC Check 1
LRC Check 0
END 1
END 0
Address
Function
Starting data address
Number of data
(count by word)
CRC CHK Low
CRC CHK High
a pointer to the message buffer
the quantity of bytes in the message buffer
'F'
'6'
CR
LF
01H
03H
21H
02H
00H
02H
6FH
F7H
Revision June 2008, 04EE, SW--PW V1.11/CTL V2.11