University:
Eastern Kentucky University
Course:
CSC 189 | Computing Concepts and Programming
Academic year:

2021
Views:

99

Pages:

4
Author:

5prinzg1s

CHAPTER 2 Short introduction 2.1 Opening serial ports Open port at “9600,8,N,1”, no timeout: >>> >>> >>> >>> >>> import serial ser = serial.Serial('/dev/ttyUSB0') # open serial port print(ser.name) # check which port was really used ser.write(b'hello') # write a string ser.close() # close port Open named port at “19200,8,N,1”, 1s timeout: >>> with serial.Serial('/dev/ttyS1', 19200, timeout=1) as ser: ... x = ser.read() # read one byte ... s = ser.read(10) # read up to ten bytes (timeout) ... line = ser.readline() # read a '\n' terminated line Open port at “38400,8,E,1”, non blocking HW handshaking: >>> ser = serial.Serial('COM3', 38400, timeout=0, ... parity=serial.PARITY_EVEN, rtscts=1) >>> s = ser.read(100) # read up to one hundred bytes ... # or as much is in the buffer 2.2 Configuring ports later Get a Serial instance and configure/open it later: >>> ser = serial.Serial() >>> ser.baudrate = 19200 (continues on next page) pySerial Documentation, Release 3.4 (continued from previous page) >>> ser.port = 'COM1' >>> ser Serial(port='COM1', baudrate=19200, bytesize=8, parity='N', ˓→stopbits=1, timeout=None, xonxoff=0, rtscts=0) >>> ser.open() >>> ser.is_open True >>> ser.close() >>> ser.is_open False Also supported with context manager: with serial.Serial() as ser: ser.baudrate = 19200 ser.port = 'COM1' ser.open() ser.write(b'hello') 2.3 Readline Be careful when using readline(). Do specify a timeout when opening the serial port otherwise it could block forever if no newline character is received. Also note that readlines() only works with a timeout. readlines() depends on having a timeout and interprets that as EOF (end of file). It raises an exception if the port is not opened correctly. Do also have a look at the example files in the examples directory in the source distribution or online. Note: The eol parameter for readline() is no longer supported when pySerial is run with newer Python versions (V2.6+) where the module io is available. 2.3.1 EOL To specify the EOL character for readline() or to use universal newline mode, it is advised to use io.TextIOWrapper: import serial import io ser = serial.serial_for_url('loop://', timeout=1) sio = io.TextIOWrapper(io.BufferedRWPair(ser, ser)) sio.write(unicode("hello\n")) sio.flush() # it is buffering. required to get the data out *now* hello = sio.readline() print(hello == unicode("hello\n")) Chapter 2. Short introduction pySerial Documentation, Release 3.4 2.4 Testing ports 2.4.1 Listing ports python -m serial.tools.list_ports will print a list of available ports. It is also possible to add a regexp as first argument and the list will only include entries that matched. Note: The enumeration may not work on all operating systems. It may be incomplete, list unavailable ports or may lack detailed descriptions of the ports. 2.4.2 Accessing ports pySerial includes a small console based terminal program called serial.tools.miniterm. It can be started with python -m serial.tools.miniterm (use option -h to get a listing of all options). 2.4. Testing ports pySerial Documentation, Release 3.4 Chapter 2. Short introduction