ASDA-A2 Chapter 9 Communications
9-14 Revision February, 2017
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):
Start ‘:’
Slave address
‘7’
‘F’
Function
‘0’
‘3’
Starting data address
‘0’
‘5’
‘C’
‘4’
Number of data
‘0’
‘0’
‘0’
‘1’
LRC Check
‘B’
‘4’
End 1 (0DH)(CR)
End 0 (0AH)(LF)
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.
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