Python通过snap7库与西门子S7-1200建立S7通信,读写存储器数据,顺便写个流水灯
阅读原文时间:2023年07月10日阅读:1

snap7 是一个基于以太网与S7系列的西门子PLC通讯的开源库。

支持包括S7系列的S7-200、S7-200 Smart、S7-300、S7-400、S7-1200以及S7-1500的以太网通信。

适用系统
支持32/64位英特尔/ AMD的所有平台。
例如:Windows ( 除了 windows Me和95);Linux和类Linux(树莓派,UBeagleBone Black,DOO 等);BSD;Oracle Solaris ;Apple OSX

支持语言
Pascal;C#;C++;C;LabVIEW;Python;Node.js;Java,其中介绍比较多的是Python。

snap7官方网站

http://snap7.sourceforge.net/

https://pypi.org/project/python-snap7/

https://python-snap7.readthedocs.io/en/latest/

西门子S7系列PLC采用以下两种通讯方式:
1) 开放式的TCP\IP,可以用于连接PLC与其他非西门子硬件
2) 西门子自己开发的S7 Protocol以太网通讯协议,用于西门子内部硬件通讯

这两者的传输报文是不一样的,如下图:

西门子数存储到二进制时方式是大端模式(BIG-Endian),而我们的普通电脑常常为小端模式(Liitle-Endian)。
大端模式是指数据的位保存在内存的地址中,而数据的高位保存在内存的低地址中.
小端模式是指数据的位保存在内存的地址中,而数据的高位保存在内存的高地址中。
例如:双字 DWORD 0X2F11214C
PLC

PC

所以数据需要进行转换。

pip install python-snap7

笔者使用的是64位Python3.6.4和python-snap7 1.1.0,安装完成后,环境就算搭建好了。

对于32位Python,需要将Snap7官网下载的Win32目录下的文件,复制到Python的安装根目录下,如下图所示:

https://sourceforge.net/projects/snap7/files/1.4.2/snap7-full-1.4.2.7z/download

通过一个连接测试代码试试,判断下环境是否搭建正常。

注意自己新建的文件名不能是snap7,会和库文件冲突!

import snap7
client = snap7.client.Client()
client.connect('192.168.0.1', 0, 1)
client.disconnect()

如果是下图提示,则环境正常(192.168.0.1的PLC不存在)。

如果是下图提示,则环境异常(snap7库安装不正确)。

4.1配置S7-1200

环境搭建正常后,在正式建立通信前PLC还需做些配置工作,主要是开发自身的读写权限。具体参照下图配置:

设置访问级别

设置DB块的属性

通过上述配置,PLC可以正常通信了。

4.2使用snap7读写存储器

python-snap7重要的两个方法是read_area和write_area,通过这两个方法就能读和写PLC的对应存储地址。

摘自client.py

def read_area(self, area: Areas, dbnumber: int, start: int, size: int) -> bytearray:
"""Reads a data area from a PLC
With it you can read DB, Inputs, Outputs, Merkers, Timers and Counters.

Args:  
    area: area to be read from.  
    dbnumber: number of the db to be read from. In case of Inputs, Marks or Outputs, this should be equal to 0.  
    start: byte index to start reading.  
    size: number of bytes to read.

Returns:  
    Buffer with the data read.

Raises:  
    :obj:\`ValueError\`: if the area is not defined in the \`Areas\`

Example:  
    >>> import snap7  
    >>> client = snap7.client.Client()  
    >>> client.connect("192.168.0.1", 0, 0)  
    >>> buffer = client.read\_area(snap7.types.Areas.DB, 1, 10, 4)  # Reads the DB number 1 from the byte 10 to the byte 14.  
    >>> buffer  
    bytearray(b'\\\\x00\\\\x00')  
"""  
if area not in Areas:  
    raise ValueError(f"{area} is not implemented in snap7.types")  
elif area == Areas.TM:  
    wordlen = WordLen.Timer  
elif area == Areas.CT:  
    wordlen = WordLen.Counter  
else:  
    wordlen = WordLen.Byte  
type\_ = snap7.types.wordlen\_to\_ctypes\[wordlen.value\]  
logger.debug(  
    f"reading area: {area.name} dbnumber: {dbnumber} start: {start}: amount {size}: wordlen: {wordlen.name}={wordlen.value}")  
data = (type\_ \* size)()  
result = self.\_library.Cli\_ReadArea(self.\_pointer, area.value, dbnumber, start,  
                                    size, wordlen.value, byref(data))  
check\_error(result, context="client")  
return bytearray(data)

@error_wrap
def write_area(self, area: Areas, dbnumber: int, start: int, data: bytearray) -> int:
"""Writes a data area into a PLC.

Args:  
    area: area to be write.  
    dbnumber: number of the db to be write to. In case of Inputs, Marks or Outputs, this should be equal to 0.  
    start: byte index to start writting.  
    data: buffer to be write.

Returns:  
    Snap7 error code.

Exmaple:  
    >>> import snap7  
    >>> client = snap7.client.Client()  
    >>> client.connect("192.168.0.1", 0, 0)  
    >>> buffer = bytearray(\[0b00000001\])  
    >>> client.write\_area(snap7.types.Areas.DB, 1, 10, buffer)  # Writes the bit 0 of the byte 10 from the DB number 1 to TRUE.  
"""  
if area == Areas.TM:  
    wordlen = WordLen.Timer  
elif area == Areas.CT:  
    wordlen = WordLen.Counter  
else:  
    wordlen = WordLen.Byte  
type\_ = snap7.types.wordlen\_to\_ctypes\[WordLen.Byte.value\]  
size = len(data)  
logger.debug(f"writing area: {area.name} dbnumber: {dbnumber} start: {start}: size {size}: "  
             f"wordlen {wordlen.name}={wordlen.value} type: {type\_}")  
cdata = (type\_ \* len(data)).from\_buffer\_copy(data)  
return self.\_library.Cli\_WriteArea(self.\_pointer, area.value, dbnumber, start,  
                                   size, wordlen.value, byref(cdata))

《SIMATIC S7-1200 可编程控制器系统手册》节4.2.1有如下描述:

PLC的数据存储通过“变量”的形式与存储区间关联,分为输入(I)、输出(O)、位存储(M)和数据块(DB)。程序在访问对应(I/O)存储区时,是通过访问CPU的过程映像对相应地址进行操作的。具体对应关系如下:

故python-snap7中定义的Areas含义为

'PE': 0x81, #input

'PA': 0x82, #output

'MK': 0x83, #bit memory

'DB': 0x84, #DB

'CT': 0x1C, #counters

'TM': 0x1D, #Timers

现在离读写PLC还差最后一步,就是起始地址如何确定呢?

对于M3.4,对应的就是M(0x83),起始地址是3,对应bit位是4。

4.3数据存储地址

https://support.industry.siemens.com/cs/document/57374718

1、BIT        :位是存储空间的最小单位;
2、BYTE    :字节,由 8 个位组成;
3、WORD  :字,由2个字节组成,共16个位。
4、DWORD:双字,由2个字组成,共32个位。
第二:绝对地址寻址(同一存储空间)
M0.0 位   :     M            0         .    0
                   存储区  字节地址     位号
MB0 字节:     M            B              0
                    存储区  字节寻地     字节起始地址
                    含 M0.0-M0.7 共 8个位
MW0   字:      M           W              0
                    存储区    字寻地      字节起始地址
                    含MB0、MB1, 即M0.0-M0.7以及 M1.0-M1.7 共 16个位
MD0 双字:     M           D              0
                    存储区    双字寻地      字节起始地址
                    含MB0、MB1、MB2、MB3, 即M0.0-M3.7共 32 个位

4.4读写示例

import struct
import time
import snap7

def plc_connect(ip, rack=0, slot=1):
'''
连接初始化
:param ip:
:param rack: 通常为0
:param slot: 根据plc安装,一般为0或1
:return:
'''
client = snap7.client.Client()
client.connect(ip, rack, slot)
return client

def plc_con_close(client):
"""
连接关闭
:param client:
:return:
"""
client.disconnect()

def test_mk10_1(client):
"""
测试M10.1
:return:
"""
area = snap7.types.Areas.MK
dbnumber = 0
start = 10
amount = 1
print('初始值',end='')
mk_data = client.read_area(area, dbnumber, start, amount)
print(mk_data)#struct.unpack('!c', mk_data)
print('置1')
client.write_area(area, dbnumber, start, b'\x01')
print('当前值',end='')
mk_cur = client.read_area(area, dbnumber, start, amount)
print(mk_cur)

def test_mk_w201(client):
"""
测试MW201,数据类型为word
:param client:
:return:
"""
area = snap7.types.Areas.MK
dbnumber = 0
amount = 2
start = 201
print(u'初始值')
mk_data = client.read_area(area, dbnumber, start, amount)
print(struct.unpack('!h', mk_data))
print(u'置12')
client.write_area(area, dbnumber, start, b'\x12')
print(u'当前值')
mk_cur = client.read_area(area, dbnumber, start, amount)
print(struct.unpack('!h', mk_cur))
time.sleep(3)
print(u'置3')
client.write_area(area, dbnumber, start, b'\x02')
print(u'当前值')
mk_cur = client.read_area(area, dbnumber, start, amount)
print(struct.unpack('!h', mk_cur))

def test_q0_0(client):
"""
测试Q0.0,会使其输出高电平
:return:
"""
area = snap7.types.Areas.PA
dbnumber = 0
start = 0
amount = 1
print('初始值',end='')
mk_data = client.read_area(area, dbnumber, start, amount)
print(mk_data)#struct.unpack('!c', mk_data)
print('置1')
client.write_area(area, dbnumber, start, b'\x01')
print('当前值',end='')
mk_cur = client.read_area(area, dbnumber, start, amount)
print(mk_cur)

def test_MD1012(client):
"""
测试MD1012,数据类型为real
:param client:
:return:
"""
area = snap7.types.Areas.MK
dbnumber = 0 # 读取的DB块序号。当读取的地址为I/Q/M时,序号为0
amount = 4
start = 1012
mk_data = client.read_area(area, dbnumber, start, amount)
print(struct.unpack('>f', mk_data)[0])

if __name__ == "__main__":
client_fd = plc_connect('192.168.0.2')
# test_mk10_1(client_fd)
# test_mk_w201(client_fd)
test_q0_0(client_fd)
plc_con_close(client_fd)

'''
'PE': 0x81, #input, I
'PA': 0x82, #output, Q
'MK': 0x83, #bit memory, M
'DB': 0x84, #DB, DBX
'CT': 0x1C, #counters
'TM': 0x1D, #Timers
'''

也可通过db_read()和db_write()读写DB块

import snap7
client = snap7.client.Client()
client.connect('192.168.0.2', 0, 1)
plc_db1 = client.db_read(1, 0, 3) # 读取数据块db1,起始字节,读取长度
print(plc_db1) # hex(plc_db1[0])
client.db_write(1, 0, b'\x11') # 写入数据块db1,起始字节,数据hex
plc_db1 = client.db_read(1, 0, 3) # 读取数据块db1,起始字节,读取长度
print(plc_db1)
client.disconnect()

读写MW变量时,要在变量表中先创建变量,并烧录进S7-1200

import struct
import time
import snap7

def plc_connect(ip, rack=0, slot=1):
'''
连接初始化
:param ip:
:param rack: 通常为0
:param slot: 根据plc安装,一般为0或1
:return:
'''
client = snap7.client.Client()
client.connect(ip, rack, slot)
return client

def plc_con_close(client):
"""
连接关闭
:param client:
:return:
"""
client.disconnect()

def ledtrip(client):
"""
跑马灯,使Q0.0~5循环亮起
:return:
"""
area = snap7.types.Areas.PA
dbnumber = 0
start = 0
delayTime = 0.5
for i in range(10):
client.write_area(area, dbnumber, start, bytearray([0b00000001]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, bytearray([0b00000010]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, bytearray([0b00000100]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, bytearray([0b00001000]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, bytearray([0b00010000]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, bytearray([0b00100000]))
time.sleep(delayTime)
client.write_area(area, dbnumber, start, b'\x00')

if __name__ == "__main__":
client_fd = plc_connect('192.168.0.2')
ledtrip(client_fd)
plc_con_close(client_fd)

https://pypi.org/project/python-snap7/

https://python-snap7.readthedocs.io/en/latest/

https://blog.csdn.net/zxpbuct/article/details/80079698

https://blog.csdn.net/lcb411/article/details/101147181

https://www.toutiao.com/a6589203413941092868

http://www.6dm.club/index.php/2018/04/07/

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