Delta ASDA-A3 Series User Manual page 611

MODBUS Communication
Communication data structure
Definitions for the data frames in the two modes are as follows:
9
ASCII mode:
Start
Slave Address
Function
Data (n-1)
.......
Data (0)
LRC
End 1
End 0
In ASCII communication mode, the message starts with a colon ‟:" (ASCII code: 3AH). The ADR
consists of two characters in ASCII code. The message ends with CR (Carriage Return) and LF
(Line Feed). The codes for data such as communication address, function code, data content,
and LRC error checking (LRC: Longitudinal Redundancy Check) are between the start
character and the end code.
RTU mode:
Start
Slave Address
Function
Data (n-1)
.......
Data (0)
CRC
End 1
In RTU communication mode, the message starts and ends with silent intervals. The codes for
data such as communication address, function code, data content, and CRC error checking
(CRC: Cyclical Redundancy Check) are between the start and end intervals.
9-6
Start character ‟:" (3AH)
Communication address: 1 byte consists of 2 ASCII codes
Function code: 1 byte consists of 2 ASCII codes
Data content: n word = 2n-byte consists of n x 4 ASCII codes, n ≤ 10
Error check: 1 byte consists of 2 ASCII codes
End code 1: (0DH) (CR)
End code 0: (0AH) (LF)
A silent interval of more than 10 ms
Communication address: 1 byte
Function code: 1 byte
Data content: n-word = 2n-byte, n ≤ 10
Error check: 1 byte
A silent interval of more than 10 ms
ASDA-A3