Modbus Communication Protocol - Delta ASDA-A2 Series User Manual

Chapter 9 Communications

9.3 MODBUS Communication Protocol

When using RS-232/485 serial communication interface, each ASDA-A2 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-A2 series
AC servo drives can be set up to communicate on a MODBUS network 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:
When AC servo drives are set up to communicate on a MODBUS network using ASCII
(American Standard Code for Information Interchange) mode, each 8–bit data in a message is
sent as two ASCII characters between the master and the slave. For example, a 1-byte data:
64 Hex, shown as '64' in ASCII, consists of '6' (36Hex) and '4' (34Hex).
ASCII Characters:
Character '0'
ASCII code 30H
Character '8'
ASCII code 38H
RTU Mode:
When AC servo drives are set up to communicate on a MODBUS network using RTU (Remote
Terminal Unit) mode, each 8-bit data is the combination of two 4-bit hexadecimal characters.
For example, a 1-byte data: 64 Hex. Comparing to ASCII mode, the transmission speed of RTU
mode is better.

Data Format
10-bit character frame (For 7-bit character)
7N2
Start
bit
7E1
Start
bit
Revision September 2012
'1' '2'
31H 32H
'9' 'A'
39H 41H
0 1 2
7-data bits
10-bits character frame
0 1 2
7-data bits
10-bits character frame
'3' '4' '5'
33H 34H 35H
'B' 'C' 'D'
42H 43H 44H
3 4 5
3 4 5
'6' '7'
36H 37H
'E' 'F'
45H 46H
Stop
Stop
6
bit
bit
Even
Stop
6
parity
bit
A2
ASDA-
9-7