python调用串口_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, seeLICENSE.txtfor more details.

Theproject page on SourceForgeand here is theSVN repositoryand theDownload Page.

The homepage is onhttp://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 theDownload 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(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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