Check Sum; Crc (Cyclical Redundancy Check) - Delta Electronics AC Motor Drive VFD-VE Series User Manual

3.4 Check sum

ASCII mode:
LRC (Longitudinal Redundancy Check) is calculated by summing up, module 256, the values of the
bytes from ADR1 to last data character then calculating the hexadecimal representation of the 2's-
complement negation of the sum.
For example, reading 1 word from address 0401H of the AC drive with address 01H.
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
Revision August 2008, 03VE, SW V2.04
content
CRC Check Low
CRC Check High
Address 1
Address 0
Function 1
Function 0
Starting data address
Number of data
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
A0H
'9'
'A'
STX
Chapter 4 Parameters|
':'
'0'
'1'
'0'
'3'
'0'
'4'
'0'
'1'
'0'
'0'
'0'
'1'
'F'
'6'
CR
LF
01H
03H
21H
02H
00H
02H
6FH
F7H
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