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Chapter 5 Parameters|VFD-S Series
Revision August 2006, SE08, SW V2.61 5-69
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
STX ‘:’
‘0’ ADR 1
ADR 0
‘1’
‘0’ CMD1
CMD0
‘3’
‘0’
‘4’
‘0’
Starting data address
‘1’
‘0’
‘0’
‘0’
Number of data
‘1’
‘F’ LRC CHK 1
LRC CHK 0
‘6’
CR END1
END0
LF
01H+03H+04H+01H+00H+01H=0AH, the 2’s-complement negation of 0AH is F6
H.
RTU mode:
ADR
01H
CMD 03H
21H Starting address
02H
00H Number of data
(count by word)
02H
CRC CHK Low 6FH
CRC CHK High F7H
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.