[Webinar] QtSerialBus: Using Modbus and CAN bus with Qt

© Integrated Computer Solutions, Inc. All Rights Reserved
QtSerialBus: Using Modbus
and CAN bus with Qt
Jeff Tranter <jtranter@ics.com>
Integrated Computer Solutions, Inc.

Agenda
• What is CAN bus?
• What is Modbus?
• The QtSerialBus Module
• What Hardware and Platforms are Supported?
• Qt APIs
• Code Examples
• Demonstration
• Areas of Possible Future Work
• Summary
• References

What is CAN bus?
• Controller Area Network bus.
• Bus standard that allows microcontrollers and devices to communicate
with each other in applications without a host computer.
• Multi-master serial bus where all nodes are connected to each other
through a two wire bus.
• Message-based protocol.
• Originally designed for multiplexed electrical wiring within automobiles,
but also used in many other contexts.

What is CAN bus?

What is Modbus?
• Serial communications protocol commonly used
for connecting industrial electronic devices.
• Allows communication among multiple devices
connected to the same network, often to connect
a supervisory computer with a remote terminal
unit in Supervisory Control and Data Acquisition
(SCADA) systems.
• Originally developed by Modicon in 1979 for use
with its programmable logic controllers (PLCs).

What is Modbus?

The QtSerialBus Module
• New module introduced as technical preview in Qt 5.6.0.
• Supports CAN bus and Modbus.
• May support other serial protocols in the future.
• Licensed like most Qt modules (LGPLv3, GPLv2, GPLv3 or commercial).
• git repo: http://code.qt.io/cgit/qt/qtserialbus.git
• Main developers and maintainers are Alex Blasche (CAN bus) and Karsten
Heimrich (Modbus) of The Qt Company.

What Hardware and Platforms are Supported?
For CAN bus, currently supports the following back ends:
• SocketCAN, which uses Linux sockets and open source drivers.
• Peak CAN, which supports PCAN adaptors from PEAK-System Technik
GmbH.
• TinyCAN, with support for Tiny-CAN adapters from MHS Elektronik.
• VectorCAN, supporting Vector Informatik CAN adapters.

What Hardware and Platforms are Supported?
For Modbus:
• One implementation (not a plugin) which doesn't depend on any external
libraries.
• Uses Qt's QtSerialPort and networking APIs.
• Supports RTU (serial) and TCP (Ethernet) communications.

Qt APIs
• C++ only, no QML
• To add to qmake projects: QT += serialbus
• Module include file: #include <QtSerialBus>
• logging categories:
• qt.modbus (standard)
• qt.modbus.lowlevel (low-level packets)

Qt APIs - CAN bus
Six classes:
QcanBus - Handles registration and creation of bus backends
QcanBusDevice::Filter - Defines a filter for CAN bus messages
QcanBusDevice - The interface class for CAN bus
QcanBusFactory - Factory class used as the plugin interface
QcanBusFrame - Container class representing a single CAN frame
QcanBusFrame::TimeStamp - Timestamp information with µsec precision

Qt APIs - Modbus
14 classes:
QModbusClient - The interface to send Modbus requests
QmodbusDataUnit - Container class representing entries in Modbus
register
QmodbusDevice - base class for QModbusServer and QModbusClient
QmodbusDeviceIdentification - Container class representing the physical
and functional description of a Modbus server
QmodbusExceptionResponse - Container class containing the function and
error code inside a Modbus ADU
QmodbusPdu - Abstract container class containing the function code and
payload that is stored inside a Modbus ADU

Qt APIs – Modbus (cont'd)
QmodbusRequest - Container class containing the function code and
QmodbusResponse - Container class containing the function code and
QmodbusReply - Contains the data for a request sent with a
QModbusClient derived class
QmodbusRtuSerialMaster - Represents a Modbus client that uses a serial
bus for its communication with the Modbus server
QmodbusRtuSerialSlave - Represents a Modbus server that uses a serial
port for its communication with the Modbus client

Qt APIs – Modbus (cont'd)
QmodbusServer - The interface to receive and process Modbus requests
QmodbusTcpClient - The interface class for Modbus TCP client device
QmodbusTcpServer - Represents a Modbus server that uses a TCP server
for its communication with the Modbus client

Code Examples - CAN bus
Basic Steps:
1. Create a device, specifying plugin and device name.
2. Connect.
3. Create data frames.
4. Send data frames.
5. Disconnect when done.
QCanBusDevice emits signals: errorOccurred, framesReceived, framesWritten,
stateChanged. To receive frames, connect to signal framesReceived.

// Create device.
QCanBusDevice *device = QCanBus::instance()->createDevice("socketcan", "vcan0");
if (device != nullptr) {
qDebug() << "Created device, state is:" << device->state();
} else {
qFatal("Unable to create CAN device.");
}
// Connect.
if (device->connectDevice()) {
qDebug() << "Connected, state is:" << device->state();
} else {
qDebug() << "Connect failed, error is:" << device->errorString();
}

Code Examples - CAN bus (cont'd)
// Create a data frame.
QCanBusFrame frame(QCanBusFrame::DataFrame, "12345");
// Send it.
if (device->writeFrame(frame)) {
qDebug() << "Wrote frame, state is:" << device->state();
} else {
qDebug() << "Write failed, error is:" << device->errorString();
}
// Disconnect.
device->disconnectDevice();
qDebug() << "Disconnected, state is:" << device->state();

On Linux there is a virtual CAN driver for testing purposes which can be
loaded and created as below:
sudo modprobe can
sudo modprobe can_raw
sudo modprobe vcan
sudo ip link add dev vcan0 type vcan
sudo ip link set up vcan0
ip link show vcan0
3: vcan0: <NOARP,UP,LOWER_UP> mtu 16 qdisc noqueue state UNKNOWN
link/can

More Complete Example – CAN bus

Code Examples - Modbus
• Unlike CAN bus which is peer to peer, Modbus is client/server.
• Client sends request and gets response from server.
• Master/Slave arrangement where the Master is a Client and the Slave is a
Server.
• Confusing terminology: there is a single Modbus client (master) and
multiple Modbus servers (slaves).
• Support for serial devices and TCP network devices.

QObject
QModbusDevice
QModbusClient QModbusServer
QModbusSerialMaster QModbusTcpClient QModbusRtuSerialSlave QModbusTcpServer

Basic steps for a TCP client (others are similar):
1. Create a QModbusTcpClient()
2. Set connection parameters with setConnectionParameter()
3. Connect using connectDevice()
4. Call as needed:
sendRawRequest()
sendReadRequest()
sendReadWriteRequest()
sendWriteRequest()
4. When done, call disconnectDevice()

// Create device.
QModbusTcpClient *device = new QModbusTcpClient();
if (device != nullptr) {
qDebug() << "Created device, state is:" << device->state();
} else {
qFatal("Unable to create Modbus TCP client device.");
}
// Set connection parameters. Defaults to local host port 502.
// Instead use TCP port 1502 as it is non-privileged.
device->setConnectionParameter(QModbusDevice::NetworkPortParameter, 1502);
// Connect.
if (device->connectDevice()) {
qDebug() << "Connected, state is:" << device->state();
} else {
qDebug() << "Connect failed, error is:" << device->errorString();
}

Code Examples – Modbus (cont'd)
// Create ADU.
QVector<quint16> data(4);
QModbusDataUnit adu(QModbusDataUnit::Coils, 1, data);
// Send read request to a server at address 1.
QModbusReply *reply = device->sendReadRequest(adu, 1);
if (reply != nullptr) {
qDebug() << "Sent read request, state is:" << device->state();
qDebug() << reply;
} else {
qDebug() << "Send of read request failed, error is:" << device->errorString();
}
// Disconnect.
device->disconnectDevice();
qDebug() << "Disconnected, state is:" << device->state();

More Complete Example - Modbus

Documentation

Qt Code Examples

Areas of Possible Future Work
• APIs final in Qt 5.8.0
• Support/plugins for more hardware back ends
• Higher level protocols?

Summary

References
1. https://en.wikipedia.org/wiki/CAN_bus
2. https://en.wikipedia.org/wiki/Modbus
3. https://doc-snapshots.qt.io/qt5-dev/qtserialbus-index.html
4. http://code.qt.io/cgit/qt/qtserialbus.git/
5. http://www.modbus.org
6. http://opengarages.org
7. ftp://ftp.ics.com/pub/pickup/qtserialbusexamples.zip

Questions?

[Webinar] QtSerialBus: Using Modbus and CAN bus with Qt

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[Webinar] QtSerialBus: Using Modbus and CAN bus with Qt