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python通过pyserial读写串口

时间:2013-08-17 14:58来源:quanpower 作者:本站 举报 点击:

 因为有个需要用有源RFID搞资产管理的项目,需要用python读取读卡器的串口内容。于是装了pyserial模块,用了下很方便,整理下常用功能


一、

为了使用python操作串口,首先需要下载相关模块:

 pyserial (http://pyserial.wiki.sourceforge.net/pySerial)

 pywin32 (http://sourceforge.net/projects/pywin32/)


2,十六进制显示

十六进制显示的实质是把接收到的字符诸葛转换成其对应的ASCII码,然后将ASCII码值再转换成十六进制数显示出来,这样就可以显示特殊字符了。

在这里定义了一个函数,如hexShow(argv),代码如下:


[python] view plain copy


import serial  
  
def hexShow(argv):  
    result = ''  
    hLen = len(argv)  
    for i in xrange(hLen):  
        hvol = ord(argv[i])  
        hhex = '%02x'%hvol  
        result += hhex+' '  
    print 'hexShow:',result  
  
t = serial.Serial('com12',9600)  
print t.portstr  
strInput = raw_input('enter some words:')  
n = t.write(strInput)  
print n  
str = t.read(n)  
print str  
hexShow(str) 



===================================================================================================================================


3,十六进制发送

十六进制发送实质是发送十六进制格式的字符串,如'\xaa','\x0b'。重点在于怎么样把一个字符串转换成十六进制的格式,有两个误区:

1)'\x'+'aa'是不可以,涉及到转义符反斜杠

2)'\\x'+'aa'和r'\x'+'aa'也不可以,这样的打印结果虽然是\xaa,但赋给变量的值却是'\\xaa'


 这里用到decode函数,


[python] view plain copy


list='aabbccddee'  
hexer=list.decode("hex")  
print  hexer  




需要注意一点,如果字符串list的长度为奇数,则decode会报错,可以按照实际情况,用字符串的切片操作,在字符串的开头或结尾加一个'0'

 

假如在串口助手以十六进制发送字符串"abc",那么你在python中则这样操作“self.l_serial.write(”\x61\x62\x63") ”

当然,还有另外一个方法:


[python] view plain copy


strSerial = "abc"  
strHex = binascii.b2a_hex(strSerial)  
#print strHex  
strhex = strHex.decode("hex")  
#print strhex  
self.l_serial.write(strhex);  



同样可以达到相同目的。

那么,串口方面的就整理完了



Overview

This module encapsulates the access for the serial port. It provides backends for Python running on Windows, Linux, BSD (possibly any POSIX compliant system), Jython and IronPython (.NET and Mono). The module named "serial" automatically selects the appropriate backend. 

It is released under a free software license, see LICENSE.txt for more details. 
(C) 2001-2008 Chris Liechti cliechti@gmx.net 

The project page on SourceForge and here is the SVN repository and the Download Page
The homepage is on http://pyserial.sf.net/ 

Features


same class based interface on all supported platforms
access to the port settings through Python 2.2+ properties
port numbering starts at zero, no need to know the port name in the user program
port string (device name) can be specified if access through numbering is inappropriate
support for different bytesizes, stopbits, parity and flow control with RTS/CTS and/or Xon/Xoff
working with or without receive timeout
file like API with "read" and "write" ("readline" etc. also supported)
The files in this package are 100% pure Python. They depend on non standard but common packages on Windows (pywin32) and Jython (JavaComm). POSIX (Linux, BSD) uses only modules from the standard Python distribution)
The port is set up for binary transmission. No NULL byte stripping, CR-LF translation etc. (which are many times enabled for POSIX.) This makes this module universally useful.



Requirements


Python 2.2 or newer
pywin32 extensions on Windows
"Java Communications" (JavaComm) or compatible extension for Java/Jython



Installation


from source

Extract files from the archive, open a shell/console in that directory and let Distutils do the rest: 
python setup.py install 

The files get installed in the "Lib/site-packages" directory. 

easy_install

An EGG is available from the Python Package Index: http://pypi.python.org/pypi/pyserial 
easy_install pyserial 

windows installer

There is also a Windows installer for end users. It is located in the Download Page 
Developers may be interested to get the source archive, because it contains examples and the readme. 

Short introduction

Open port 0 at "9600,8,N,1", no timeout 
>>> import serial
>>> ser = serial.Serial(0)  # open first serial port
>>> print ser.portstr       # check which port was really used
>>> ser.write("hello")      # write a string
>>> ser.close()             # close port
Open named port at "19200,8,N,1", 1s timeout 
>>> ser = serial.Serial('/dev/ttyS1', 19200, timeout=1)
>>> x = ser.read()          # read one byte
>>> s = ser.read(10)        # read up to ten bytes (timeout)
>>> line = ser.readline()   # read a '\n' terminated line
>>> ser.close()
Open second port at "38400,8,E,1", non blocking HW handshaking 
>>> ser = serial.Serial(1, 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

Get a Serial instance and configure/open it later 

>>> ser = serial.Serial()
>>> ser.baudrate = 19200
>>> ser.port = 0
>>> ser
Serial<id=0xa81c10, open=False>(port='COM1', baudrate=19200, bytesize=8, parity='N', stopbits=1, timeout=None, xonxoff=0, rtscts=0)
>>> ser.open()
>>> ser.isOpen()
True
>>> ser.close()
>>> ser.isOpen()
False

Be carefully 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. 

Examples

Please look in the SVN Repository. There is an example directory where you can find a simple terminal and more. 
http://pyserial.svn.sourceforge.net/viewvc/pyserial/trunk/pyserial/examples/ 

Parameters for the Serial class

ser = serial.Serial(
port=None,              # number of device, numbering starts at
# zero. if everything fails, the user
# can specify a device string, note
# that this isn't portable anymore
# if no port is specified an unconfigured
# an closed serial port object is created
baudrate=9600,          # baud rate
bytesize=EIGHTBITS,     # number of databits
parity=PARITY_NONE,     # enable parity checking
stopbits=STOPBITS_ONE,  # number of stopbits
timeout=None,           # set a timeout value, None for waiting forever
xonxoff=0,              # enable software flow control
rtscts=0,               # enable RTS/CTS flow control
interCharTimeout=None   # Inter-character timeout, None to disable
)
The port is immediately opened on object creation, if a port is given. It is not opened if port is None. 
Options for read timeout: 
timeout=None            # wait forever
timeout=0               # non-blocking mode (return immediately on read)
timeout=x               # set timeout to x seconds (float allowed)

Methods of Serial instances

open()                  # open port
close()                 # close port immediately
setBaudrate(baudrate)   # change baud rate on an open port
inWaiting()             # return the number of chars in the receive buffer
read(size=1)            # read "size" characters
write(s)                # write the string s to the port
flushInput()            # flush input buffer, discarding all it's contents
flushOutput()           # flush output buffer, abort output
sendBreak()             # send break condition
setRTS(level=1)         # set RTS line to specified logic level
setDTR(level=1)         # set DTR line to specified logic level
getCTS()                # return the state of the CTS line
getDSR()                # return the state of the DSR line
getRI()                 # return the state of the RI line
getCD()                 # return the state of the CD line

Attributes of Serial instances

Read Only: 
portstr                 # device name
BAUDRATES               # list of valid baudrates
BYTESIZES               # list of valid byte sizes
PARITIES                # list of valid parities
STOPBITS                # list of valid stop bit widths
New values can be assigned to the following attributes, the port will be reconfigured, even if it's opened at that time: 

port                    # port name/number as set by the user
baudrate                # current baud rate setting
bytesize                # byte size in bits
parity                  # parity setting
stopbits                # stop bit with (1,2)
timeout                 # timeout setting
xonxoff                 # if Xon/Xoff flow control is enabled
rtscts                  # if hardware flow control is enabled

Exceptions

serial.SerialException

Constants

parity: 
    serial.PARITY_NONE
serial.PARITY_EVEN
serial.PARITY_ODD
stopbits: 
    serial.STOPBITS_ONE
serial.STOPBITS_TWO
bytesize: 
    serial.FIVEBITS
serial.SIXBITS
serial.SEVENBITS
serial.EIGHTBITS
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