Delta ASDA-B2 Series User Manual page 283

Chapter 8 Communications
 LRC and CRC transmission Error Checking:
The error checking in ASCII communication mode is LRC (Longitudinal Redundancy
Check); CRC (Cyclical Redundancy Check) is for RTU communication mode.
The algorithm of both is as the following.
LRC (ASCII mode):
STX
ADR
CMD
Starting data address
Number of data
LRC Check
End 1
End 0
The LRC algorithm is: add all byte, round down the carry and take 2's complement.
For example, 7FH + 03H + 05H + C4H + 00H + 01H = 14CH, round down carry 1 and
take 4CH.
2's complement of 4CH is B4H.
CRC (RTU Mode):
The description of CRC is as the followings:
Step 1: Load a 16-bits register of FFFFH, which is called "CRC" register.
Step 2: (The low byte of CRC register) XOR (The first byte of command), and save
the result in CRC register.
Step 3: Right move one bit. Check the least significant bit (LSB) of CRC register.
If the bit is 1, then (CRC register) XOR (A001H).
Step 4: Return to Step 3 until Step 3 has been executed for 8 times. Go to Step 5.
Step 5: Repeat the procedure from Step 2 to Step 4 until all byte is processing.
Get the result of CRC value.
8-14
':'
'7'
'F'
'0'
'3'
'0'
'5'
'C'
'4'
'0'
'0'
'0'
'1'
'B'
'4'
(0DH)(CR)
(0AH)(LF)
ASDA-B2
Revision May, 2018