Shows how to use various features of
Terminal shows how to create a terminal for a simple serial interface by using Qt Serial Port .
This example shows the main features of the
QSerialPort class, like configuration, I/O implementation and so forth. Also, the class
QSerialPortInfo is invoked to display information about the serial ports available in the system.
QSerialPort supports two general programming approaches:
The asynchronous (non-blocking) approach. Operations are scheduled and performed when the control returns to Qt’s event loop.
QSerialPortemits a signal when the operation is finished. For example,
write()returns immediately. When the data is sent to the serial port,
The synchronous (blocking) approach. In non-GUI and multithreaded applications, the
waitFor...()functions can be called (i.e.
waitForReadyRead()) to suspend the calling thread until the operation has completed.
In this example, the asynchronous approach is demonstrated. The Blocking Receiver example illustrates the synchronous approach.
Our example contains some GUI widgets:
terminal/mainwindow.cpp) - is the main application window that contains all the working logic for the serial port programming, including configuration, I/O processing and so forth, while inheriting the
terminal/console.cpp) - is the central widget of the main window, displaying the transmitted or received data. The widget is derived from the
terminal/settingsdialog.cpp) - is a dialog for configuring the serial port, as well as for displaying the available serial ports and information about them.
The serial port is instantiated in the
MainWindow constructor. The main widget is passed as the parent, so the object deletion happens automatically according to the parent and child mechanism in Qt:
def __init__(self, parent): QMainWindow(parent), m_ui(Ui.MainWindow), m_status(QLabel), m_console(Console), m_settings(SettingsDialog), m_serial(QSerialPort(self)) ... m_serial(QSerialPort(self))
QSerialPort signal invoked in this example is
readyRead() , which shows that new data has been received and hence available:
... m_serial.readyRead.connect(self.readData) ...
Clicking on the Connect button invokes the
def openSerialPort(self): SettingsDialog.Settings p = m_settings.settings() m_serial.setPortName(p.name) m_serial.setBaudRate(p.baudRate) m_serial.setDataBits(p.dataBits) m_serial.setParity(p.parity) m_serial.setStopBits(p.stopBits) m_serial.setFlowControl(p.flowControl) if m_serial.open(QIODevice.ReadWrite): m_console.setEnabled(True) m_console.setLocalEchoEnabled(p.localEchoEnabled) m_ui.actionConnect.setEnabled(False) m_ui.actionDisconnect.setEnabled(True) m_ui.actionConfigure.setEnabled(False) showStatusMessage(tr("Connected to %1 : %2, %3, %4, %5, %6") .arg(p.name).arg(p.stringBaudRate).arg(p.stringDataBits) .arg(p.stringParity).arg(p.stringStopBits).arg(p.stringFlowControl)) else: QMessageBox.critical(self, tr("Error"), m_serial.errorString()) showStatusMessage(tr("Open error"))
In this slot, the settings are read from
SettingsDialog and an attempt is made to open and initialize the serial port accordingly. If successful, the status bar displays a message that the opening was successful with the given configuration; otherwise, a messagebox is displayed with the appropriate error code and message. If the serial port settings have never been called then the terminal attempts to open the port with the default settings: 9600 8N1.
Clicking on the Disconnect button invokes the
def closeSerialPort(self): if m_serial.isOpen(): m_serial.close() m_console.setEnabled(False) m_ui.actionConnect.setEnabled(True) m_ui.actionDisconnect.setEnabled(False) m_ui.actionConfigure.setEnabled(True) showStatusMessage(tr("Disconnected"))
In this case, handled by the closure of the serial port.
Typing characters in the console invokes the
def writeData(self, data): m_serial.write(data)
This slot sends the characters typed in the given Console widget to the serial port - see
When the serial port receives new data, the signal
readyRead() is emitted, and that signal is connected to the
def readData(self): data = m_serial.readAll() m_console.putData(data)
This slot reads the data from the serial port and displays that in the Console widget.
Clicking on the Configure button invokes the
show() slot which belongs to the
This method (
terminal/settingsdialog.cpp) displays the
SettingsDialog, in which the user can choose the desired serial port, see the information about the selected port, and set the desired parameters of the given serial port.
Running the Example#
To run the example from Qt Creator, open the Welcome mode and select the example from Examples. For more information, visit Building and Running an Example.