Python的网络编程[6] -> Modbus 协议 -> Modbus 的基本理论与 Python 实现

 1 import struct
 2 
 3 
 4 class ModbusCodeC():
 5     """
 6     This CodeC class implement partly of Modbus encode and decode
 7     The chamber only offer 03H and 06H function-code for using
 8     """
 9 
10     @staticmethod
11     def MBAP_encode():
12         transFlagHi = b‘\x00‘
13         transFlagLo = b‘\x00‘
14         protoFlag = b‘\x00\x00‘
15         length = b‘\x00\x06‘
16         unitFlag = b‘\x00‘
17         mbap = transFlagHi + transFlagLo + protoFlag + length + unitFlag
18         return mbap
19 
20     @staticmethod
21     def PDU_encode(func, regi, num=1, data=None):
22         funcList = {‘r‘: b‘\x03‘,
23                     ‘w‘: b‘\x06‘}
24         funcCode = funcList[func]
25         registerStart = struct.pack(‘!H‘, regi)
26         registerNum = struct.pack(‘!H‘, num)
27         if data and func == ‘w‘:
28             dataCode = struct.pack(‘!H‘, data)
29             pdu = funcCode + registerStart + dataCode
30             return pdu
31         pdu = funcCode + registerStart + registerNum
32         return pdu
33 
34     @staticmethod
35     def encode(func, regi, num, data=None):
36         return ModbusCodeC.MBAP_encode() + ModbusCodeC.PDU_encode(func, regi, num, data)
37 
38     @staticmethod
39     def MBAP_decode(s):
40         m = {}
41         m[‘transFlagHi‘] = s[:1]
42         m[‘transFlagLo‘] = s[1:2]
43         m[‘protoFlag‘] = s[2:4]
44         m[‘length‘] = s[4:6]
45         m[‘unitFlag‘] = s[6:]
46         return m
47         
48     @staticmethod
49     def PDU_decode(s):
50         p = {}
51         ‘‘‘
52         p[‘funcCode‘] = s[:1]
53         p[‘registerStart‘] = s[1:3]
54         p[‘registerNum‘] = s[3:5]
55         p[‘data‘] = s[5:]
56         ‘‘‘
57         # TODO: Add bit number and data length check here
58         p[‘funcCode‘] = s[:1]
59         p[‘bitNum‘] = s[1:2]
60         p[‘data‘] = s[2:]
61         return p
62 
63     @staticmethod
64     def decode(msg):
65         msg_de = {}
66         mbap, pdu = msg[:7], msg[7:]
67         msg_de[‘MBAP‘] = ModbusCodeC.MBAP_decode(mbap)
68         msg_de[‘PDU‘] = ModbusCodeC.PDU_decode(pdu)
69         return msg_de
70 
71 if __name__ == ‘__main__‘:
72     print(ModbusCodeC.encode(‘r‘, 5, 3))
73     print(ModbusCodeC.encode(‘w‘, 5, 1, 8))