用 python 的snap7库 连接西门子 200 smart

先推荐一篇知乎上的文章,讲的非常详细.  使用Snap7读写西门子S7系列PLC

但,可能存在版本不同的问题,很多地方不能正常运行.下面贴出的是测试代码:

环境 python 3.8.4 (snap7 目前需要工作在 python3.6+,我经常用的是python3.4.4,这是支持XP的最后一个版本,已确定这个版本连import snap7 都报错)

snap7  python-snap7 1.2

>>> from snap7 import client
>>> from snap7.types import areas
>>> type(areas)
<class 'snap7.common.ADict'>
>>> areas['MK']
131

# 按推荐文档连接PLC 成功
>>> plc = client.Client()
>>> plc.set_connection_type(2)
>>> plc.connect('192.168.2.1',0,1)
>>> plc.get_connected()
True
# 但读数据时报错
>>> 读出的字节组 = plc.read_area(areas['MK'],0,1,1)
Traceback (most recent call last):
  File "<pyshell#30>", line 1, in <module>
    读出的字节组 = plc.read_area(areas['MK'],0,1,1)
  File "C:\Python38\lib\site-packages\snap7\client.py", line 390, in read_area
    if area not in Areas:
  File "C:\Python38\lib\enum.py", line 315, in __contains__
    raise TypeError(
TypeError: unsupported operand type(s) for 'in': 'int' and 'EnumMeta'
# 打算读的是 200smart 的VB10,尝试用GitHub下载的源码中的例子尝试
# 但不清楚plc.db_read(0,10,1)的第一个参数应该怎么填,最后试出,对于200smart,应该填1
>>> 读出的字节组 = plc.db_read(0,10,1)
b'CLI : function refused by CPU (Unknown error)'
Traceback (most recent call last):
  File "<pyshell#31>", line 1, in <module>
    读出的字节组 = plc.db_read(0,10,1)
  File "C:\Python38\lib\site-packages\snap7\client.py", line 226, in db_read
    check_error(result, context="client")
  File "C:\Python38\lib\site-packages\snap7\common.py", line 89, in check_error
    raise RuntimeError(error)
RuntimeError: b'CLI : function refused by CPU (Unknown error)'
>>> 读出的字节组 = plc.db_read(1,10,1)
>>> 读出的字节组
bytearray(b'\x0f')

# 通过查看源码,找到了正确的 read_area()的使用办法
>>> from snap7.types import Areas
# Area.DB 指300,400,1200,1500中的DB块,也指200smart中的V区(相当于DB1)
# DB号填错,被PLC拒绝
>>> 读出的字节组 = plc.read_area(Areas.DB,0,10,1)
b'CLI : function refused by CPU (Unknown error)'
Traceback (most recent call last):
  File "<pyshell#39>", line 1, in <module>
    读出的字节组 = plc.read_area(Areas.DB,0,10,1)
  File "C:\Python38\lib\site-packages\snap7\client.py", line 403, in read_area
    check_error(result, context="client")
  File "C:\Python38\lib\site-packages\snap7\common.py", line 89, in check_error
    raise RuntimeError(error)
RuntimeError: b'CLI : function refused by CPU (Unknown error)'
# 正确读出VB10
>>> 读出的字节组 = plc.read_area(Areas.DB,1,10,1)
>>> 读出的字节组
bytearray(b'\x1f')
>>> plc.read_area(Areas.DB,1,10,1)
bytearray(b'\x0f')
>>> dir(Areas)
['CT', 'DB', 'MK', 'PA', 'PE', 'TM', '__class__', '__doc__', '__members__', '__module__']
>>> Areas.PA
<Areas.PA: 130>
>>> type(Areas.PA)
<enum 'Areas'>
>>> Areas.PE
<Areas.PE: 129>
# 尝试写入数据,在step7上验证成功
>>> 读出的字节组[0] = 0xFF
>>> plc.db_write(1,10,读出的字节组)
>>>