使用python下的pyserial进行串口测试和设备调用
硬件开发不可避免要与串口打交道，使用python下的pyserial可以使串口测试和设备调用的工作自动化。这里介绍pyserial的一些基础知识。
1、安装pyserial
linux上直接安装：
#python2 sudo pip install pyserial #或者python3 sudo pip3 install pyserial
2、Bytes与string的转换
很多串口使用的数据是byte格式，需要进行转换。
使用str.decode()将ASCII转为String的Unicode。
使用bytes.encode(str,"ASCII")将Unicode转为ASCII的byte格式。
使用string.strip()去除后面的回车、换行等无效字符。
声明：s为字符串，rm为要删除的字符序列 s.strip(rm) 删除s字符串中开头、结尾处，位于 rm删除序列的字符 s.lstrip(rm) 删除s字符串中开头处，位于 rm删除序列的字符 s.rstrip(rm) 删除s字符串中结尾处，位于 rm删除序列的字符 注意： 1. 当rm为空时，默认删除空白符（包括'\n', '\r', '\t', ' ')
3、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：
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)
4、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：
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：
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。
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 [email protected]
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