如何通过 Modbus TCP 使用“struct.pack”类型发送？

Question

我想通过 Modbus TCP 发送数据包。我想使用：

但是我不能以这种方式发送我如何发送这个数据包？（我不知道会发生什么）

req = struct.pack(

   'Something', transaction, identifier, length, unitid, func_code, reg_addr

) 

这些是我的变量：

transaction=0x01

identifier=0x00

length=[0x00,0x06]

unitid=0x01

func_code=0x03

reg_addr=[0x13,0x14,0x15]

Answer 1

首先，您可以使用具有很多功能的pymodbus库。另外struct.pack()不支持列表作为参数。0001 0000 0006 11 03 006B 0003 是 Modbus-TCP 数据包的标准示例，其中包含：0001: Transaction Identifier0000: Protocol Identifier0006: Message Length (6 bytes to follow)11: The Unit Identifier  (17 = 11 hex)03: The Function Code (read Analog Output Holding Registers)006B: The Data Address of the first register requested. (40108-40001 = 107 =6B hex)0003: The total number of registers requested. (read 3 registers 40108 to 40110)参考因此，您可以使用上述示例创建Modbus-TCP数据包：import structtransaction = 0x0001identifier = 0x0000length = 0x0006unitid = 0x11fcode = 0x03  # Holding register fcode.reg_addr = 0x006B  # Register address.count = 0x0003  # Read three register.total_pack_string = '0x{:04x}{:04x}{:04x}{:02x}{:02x}{:04x}{:04x}'.format(    transaction, identifier, length, unitid, fcode, reg_addr, count)total_pack_hex = hex(int(total_pack_string, 16))'''Or with using pack method.'''pack_ = struct.pack(   '>HHHBBHH', transaction, identifier, length, unitid, fcode, reg_addr, count)# Then send the pack_ or total_pack_hex using a TCP-Socket.[注意]：transaction 是 2Byte == 短 == Hidentifier 是 2Byte == 短 == Hlength 是 2Byte == 短 == Hunitid 是 1Byte == Bfcode 是 1Byte == Breg_addr 是 2Byte == 短 == Hcount 是 2Byte == 短 == HB 是 unsigned byteH 是 unsigned short因此，格式将是这样的 >HHHBBHH使用pymodbus等效项：from pymodbus.client.sync import ModbusTcpClientunitid = 0x11fcode = 0x03  # Holding register fcode.reg_addr = 0x006B  # Register address.count = 0x0003  # Read three register.cli = ModbusTcpClient('127.0.0.1', port=502)if cli.connect():    res = cli.read_holding_registers(reg_addr, count=count, unit=unitid)        if not res.isError():        print(res.registers)        else:        print('There is an error.')        cli.close()else:    print('Error in connection.')