blob: 85c1d312035ebbac1f74163d47b1dc95c88c037d (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
|
// Copyright (C) 2023 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*! \example modbus/client
\title Modbus Client
\ingroup qtserialbus-examples
\meta category Connectivity
\brief The example implements a Modbus client application.
The example acts as Modbus client sending Modbus request via serial line
or TCP. The shown dialog allows the definition of standard requests and
displays incoming responses.
The example must be used in conjunction with the \l {Modbus server example}
or another Modbus device which is either connected via TCP or Serial Port.
Key classes used in this example:
\list
\li \l QModbusClient
\li \l QModbusDataUnit
\li \l QModbusReply
\endlist
\image ../images/modbusclient.png
\section1 Creating a QModbusClient
An instance of \l QModbusClient is required to perform any communication.
Depending on the specified connection type, the example can instantiate
a \l QModbusRtuSerialClient (for serial communication), or a
\l QModbusTcpClient (for TCP-based communication).
\snippet modbus/client/mainwindow.cpp create_client_0
Once the client is created, use the
\l {QModbusClient::}{setConnectionParameter()} method to specify the
connection parameters. The parameters vary depending on the communication
type:
\snippet modbus/client/mainwindow.cpp create_client_1
After the client is created and all the parameters are specified, use
\l {QModbusClient::connectDevice()} to connect to Modbus network.
\section1 Reading Data
To read data from Modbus server, the client needs to specify a
server address and the parameters of objects that it wants to read:
\list
\li \l {QModbusDataUnit::}{RegisterType}
\li \l {QModbusDataUnit::startAddress}{start address}
\li \l {QModbusDataUnit::valueCount}{number of entries to read}
\endlist
The object parameters are represented by the \l QModbusDataUnit class:
\snippet modbus/client/mainwindow.cpp read_data_0
Once the parameters are collected, the
\l {QModbusClient::}{sendReadRequest()} method is used to send the actual
request. The method returns a \l QModbusReply which should be processed
in an asynchronous way, so the \l QModbusReply::finished() signal is used
to check when the reply is ready.
\snippet modbus/client/mainwindow.cpp read_data_1
Once the \l QModbusReply::finished() signal is received, the reply object
can be used to get the data or to check for read errors:
\snippet modbus/client/mainwindow.cpp read_data_2
\section1 Writing Data
To write the data to the Modbus server, the client needs to specify the
server address, and the parameters of objects that it wants to write.
As with reading the data, the \l QModbusDataUnit class is used to represent
the information about the data to be written. This time the data also
includes the desired \l {QModbusDataUnit::}{values}.
The \l {QModbusClient::}{sendWriteRequest()} method is used to write the
desired data:
\snippet modbus/client/mainwindow.cpp write_data_0
Like with reading the data, the returned \l QModbusReply object is used
to check for write errors.
\include examples-run.qdocinc
*/
|
