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Chapter 4 Parameter Settings|DD Series
4-71
‘A’
‘0’
‘9’
LRC Check
‘A’
CR
END
LF
RTU mode:
Command message: Response message:
ADR 01H ADR 01H
CMD1 10H CMD 1 10H
05H 05H
Starting data address
00H
Starting data address
00H
00H 00H
Number of data
(count by word)
02H
Number of data
(count by word)
02H
Number of data
(count by byte)
04
CRC Check Low
41H
13H CRC Check High 04H
The first data content
88H
0FH
The second data content
A0H
CRC Check Low ‘9’
CRC Check High ‘A’
Check sum
ASCII mode:
LRC (Longitudinal Redundancy Check) is calculated by summing up, module 256 and 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,
01H+03H+21H+02H+00H+02H=29H, the 2’s-complement negation of 29H is D7H.
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.