[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 <[email protected]>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 backendsQcanBusDevice::Filter - Defines a filter for CAN bus messagesQcanBusDevice - The interface class for CAN busQcanBusFactory - Factory class used as the plugin interfaceQcanBusFrame - Container class representing a single CAN frameQcanBusFrame::TimeStamp - Timestamp information with µsec precision


Qt APIs - Modbus

14 classes:QModbusClient - The interface to send Modbus requestsQmodbusDataUnit - Container class representing entries in Modbus registerQmodbusDevice - base class for QModbusServer and QModbusClientQmodbusDeviceIdentification - Container class representing the physical and functional description of a Modbus serverQmodbusExceptionResponse - Container class containing the function and error code inside a Modbus ADUQmodbusPdu - 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 payload that is stored inside a Modbus ADUQmodbusResponse - Container class containing the function code and payload that is stored inside a Modbus ADUQmodbusReply - Contains the data for a request sent with a QModbusClient derived classQmodbusRtuSerialMaster - Represents a Modbus client that uses a serial bus for its communication with the Modbus serverQmodbusRtuSerialSlave - 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 requestsQmodbusTcpClient - The interface class for Modbus TCP client deviceQmodbusTcpServer - 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.


Code Examples - CAN bus // 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();


Code Examples - CAN bus

On Linux there is a virtual CAN driver for testing purposes which can be loaded and created as below:

sudo modprobe cansudo modprobe can_rawsudo modprobe vcansudo ip link add dev vcan0 type vcansudo ip link set up vcan0ip link show vcan03: 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

QModbusDeviceQModbusClient 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()


Code Examples - Modbus // 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_bus2. https://en.wikipedia.org/wiki/Modbus3. https://doc-snapshots.qt.io/qt5-dev/qtserialbus-index.html4. http://code.qt.io/cgit/qt/qtserialbus.git/5. http://www.modbus.org6. http://opengarages.org7. ftp://ftp.ics.com/pub/pickup/qtserialbusexamples.zip


Questions?


QtSerialBus: Using Modbus and CAN bus with Qt

Jeff Tranter <[email protected]>Integrated Computer Solutions, Inc.

[webinar] qtserialbus: using modbus and can bus with qt

Software