Chapter 8 MODBUS Communications
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ASDA-A&A+ Series
Revision April 2009
8-9
8.3 MODBUS Communication Protocol
When using RS-232/485/422 serial communication interface, each ASDA-A or ASDA-A+ series AC servo
drive has a pre-assigned communication address specified by parameter “P3-00”. The computer then
controls each AC servo drive according to its communication address. ASDA-A and ASDA-A+ series AC
servo drives can be set up to communicate on a MODBUS networks using on of the following modes: ASCII
(American Standard Code for Information Interchange) or RTU (Remote Terminal Unit). Users can select the
desired mode along with the serial port communication protocol in parameter “P3-02”.
Code Description:
ASCII Mode:
Each 8-bit data is the combination of two ASCII characters. For example, a 1-byte data: 64 Hex, shown as
‘64’ in ASCII, consists of ‘6’ (36Hex) and ‘4’ (34Hex).
The following table shows the available hexadecimal characters and their corresponding ASCII codes.
Character
‘0’
‘1’
‘2’
‘3’
‘4’
‘5’
‘6’
‘7’
ASCII
code
30H 31H 32H 33H 34H 35H 36H 37H
Character
‘8’
‘9’
‘A’
‘B’
‘C’
‘D’
‘E’
‘F’
ASCII
code
38H 39H 41H 42H 43H 44H 45H 46H
RTU Mode:
Each 8-bit data is the combination of two 4-bit hexadecimal characters. For example, a 1-byte data: 64 Hex.
Data Format:
10-bit character frame (For 7-bit character)
7N2
Start
bit
0
1
2
3
4
5
6
Stop
bit
7-data bits
10-bits character frame
Stop
bit
7E1
Even
parity
Start
bit
0
1
2
3
4
5
6
Stop
bit
7-data bits
10-bits character frame
7O1
Odd
parity
Start
bit
0
1
2
3
4
5
6
Stop
bit
7-data bits
10-bits character frame
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