Chapter 8 MODBUS Communications|ASDA-A&A+ Series
Revision April 2009 8-11
STX (Communication Start)
ASCII Mode: ā:ā character
RTU Mode: A silent interval of more than 10ms
ADR (Communication Address)
The valid communication addresses are in the range of 1 to 254.
For example, communication to AC servo drive with address 16 decimal:
ASCII Mode: ADR=ā1ā,ā0ā => ā1ā=31Hļ¼ā0ā=30H
RTU Mode: ADR = 10H
CMD (Command Codes) and DATA (Data Characters)
The format of data characters depends on the command code. The available command codes and examples
for AC servo drive are described as follows:
Command code: 03H, read N words. The maximum value of N is 10.
For example, reading continuous 2 words from starting address 0200H of AC servo drive with address 01H.
ASCII Mode:
Command message: Response message:
STX ā:ā STX ā:ā
ā0ā ā0ā
ADR
ā1ā
ADR
ā1ā
ā0ā ā0ā
CMD
ā3ā
CMD
ā3ā
ā0ā ā0ā
ā2ā
Number of data
(Count by byte)
ā4'
ā0ā ā0ā
Starting data
address
ā0ā ā0ā
ā0ā āBā
ā0ā
Contents of starting
data address
0200H
ā1ā
ā0ā ā1ā
Number of data
ā2ā āFā
āFā ā4ā
LRC Check
ā8ā
Contents of second
data address
0201H
ā0ā
End 1 (0DH)(CR) āEā
End 0 (0AH)(LF)
LRC Check
ā8ā
End 1 (0DH)(CR)
End 0 (0AH)(LF)
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