Chapter 9 Communication
ASDA-A2R Series
9-4
Revision December, 2014
9.3 MODBUS Communication Protocol
There are two modes of MODBUS networks communication, ASCII (American Standard
Code for information interchange) mode and RTU (Remote Terminal Unit) mode. Users
could set the needed communication protocol via parameter P3-02. Apart from these two
communication modes, this servo drive also supports function of 03H to access more than
one data, 06H to write one character and 10H to write multiple characters. Please refer to
the following descriptions.
Code Description
ASCII Mode:
The so-called ASCII mode is using American Standard Code for Information Interchange
(ASCII) to transmit the data. Between two stations (Master and Slave) to transmit data 64H,
the master will send
‘
6
’
which represented by 36H of ASCII code and
‘
4
’
represented
by 34H of ASCII code.
ASCII code of digit 0 to 9 and characters A to F is as follows:
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:
Every 8-bit of data is constituted by two 4-bits hexadecimal characters. If data 64H is
transmitted between two stations, it will be transmitted directly, which is more efficient than
ASCII mode.
Character Structure
Characters will be encoded into the following framing and transmitted in serial. The
checking method of different bit is as the following.
10 bits 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