ASDA-B2
Chapter 8 MODBUS Communications
Revision September 2013
8-9
RTU Mode:
Start
A silent interval of more than 10ms
Slave address
Communication address: 1-byte
Function Function
code:
1-byte
DATA(n-1)
Contents of data: n word = n x 2-byte, n
10
…….
DATA(0)
CRC
CRC check sum: 1-byte
End 1
A silent interval of more than 10ms
RTU Mode: A silent interval of more than 10ms
RTU (Remote Terminal Unit) starts from a silent signal and ends at another silent signal.
There are communication address, function code, contents of data, CRC (Cyclical
Redundancy Check) between start and end characters.
DATA (Data Characters)
The format of data characters depends on the function code. The available command
codes and examples for AC servo drive are described as follows:
Example 1
Function code: 03H, read N words (multiple words). The maximum value of N is 10.
For example, reading continuous 2 words from starting address 0200H of AC servo drive
with address 01H.
ASCII Mode:
Command message:
Response message:
Start ‘:’
Start ‘:’
Slave address
‘0’
Slave address
‘0’
‘1’
‘1’
Function
‘0’
Function
‘0’
‘3’
‘3’
Starting data
address
‘0’
Number of data
(In Byte)
‘0’
‘2’
‘4'
‘0’
Contents of
starting data
address 0200H
‘0’
‘0’
‘0’
Number of data
‘0’
‘B’
‘0’
‘1’
‘0’
Contents of
second data
address 0201H
‘1’
‘2’
‘F’
LRC Check
‘F’
‘4’
‘8’
‘0’
End 1
(0DH)(CR)
LRC Check
‘E’
End 0
(0AH)(LF)
‘8’
End 1
(0DH)(CR)
End 0
(0AH)(LF)
VARITEL INGENIERIA ELECTRONICA S.A.
[email protected] - www.varitel.com - Tel. (54) 11-4243-1171 / Fax: (54) 11-4292-7545
Manuel Baliña 456, Lomas de Zamora (B1832CCJ) Buenos Aires, Argentina.
