Modbus Communication Protocol; Code Description; Ascii Mode; Rtu Mode - Delta ASDA-A3 Series User Manual

MODBUS Communication

9.3 MODBUS communication protocol

There are two modes of MODBUS network communication: ASCII (American Standard Code for
9
Information Interchange) and RTU (Remote Terminal Unit). You can set both communication
protocols (ASCII and RTU) with the P3.002 parameter. The ASDA-A3 servo drive also supports
these functions: accessing data (03H), writing one character (06H) and writing multiple
characters (10H). Please refer to the following descriptions.

Code Description

ASCII mode:

In ASCII mode, data is transmitted in ASCII (American Standard Code for Information
Interchange) format. For instance, when transmitting "64H" between two stations (master and
slave), the master sends 36H to represent ‟6" and 34H to represent "4".
The ASCII codes for the digits 0 to 9 and the characters A to F are as follows:
ASCII code
ASCII code

RTU mode:

Every 8-bit data frame consists of two 4-bit characters (hexadecimal). For example, if "64H" is
transmitted between two stations using RTU, it is transmitted directly, which is more efficient than
ASCII mode.
Characters are encoded into the frames and transmitted in series. The method for checking each
type of frame is as follows.
10-bit character frame (for 7-bit character)
9-4
Character '0'
30H
Character '8'
38H
L
7N2
Start
0
bit
L
7E1
Start
0
bit
L
7O1
Start
0
bit
'1' '2' '3'
31H 32H 33H
'9' 'A' 'B'
39H 41H 42H
1 2 3 4
7-data bits
10-bit character frame
1 2 3 4
7-data bits
10-bit character frame
1 2 3 4
7-data bits
10-bit character frame
'4' '5' '6'
34H 35H 36H
'C' 'D' 'E'
43H 44H 45H
H H
Stop Stop
5 6
bit bit
H
Even Stop
5 6
Parity bit
H
Odd Stop
5 6
Parity bit
Revision December, 2017
ASDA-A3
'7'
37H
'F'
46H