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Chapter 8 MODBUS Communications|ASDA-B Series
Revision January 2009 8-9
11-bit character frame (For 8-bit character)
8N2
Start
bit
01
2
3456
Stop
bit
8-data bits
11-bits character frame
Stop
bit
7
8E1
Start
bit
01
2
3456
Stop
bit
8-data bits
11-bits character frame
7
Even
parity
8O1
Start
bit
01
2
3456
Stop
bit
8-data bits
11-bits character frame
7
Odd
parity
Communication Protocol:
ASCII Mode:
STX Start character’: ’ (3AH)
ADR Communication address: 1-byte consists of 2 ASCII codes
CMD Command code: 1-byte consists of 2 ASCII codes
DATA(n-1)
…….
DATA(0)
Contents of data: n word = n x 2-byte consists of n x 4 ASCII codes, n≤12
LRC Command code: 1-byte consists of 2 ASCII codes
End 1 End code 1: (0DH)(CR)
End 0 End code 0: (0AH)(LF)
RTU Mode:
STX A silent interval of more than 10ms
ADR Communication address: 1-byte
CMD Command code: 1-byte
DATA(n-1)
…….
DATA(0)
Contents of data: n word = n x 2-byte, n≤12
CRC Command code: 1-byte
End 1 A silent interval of more than 10ms