使用等效的pymodbus：

Question

我想通过Modbus TCP发送数据包。我要使用：

但是我无法通过这种方式发送该如何发送此数据包？（我不知道会有什么事

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

起初，您可以使用具有特色的pymodbus库。
另外struct.pack()不支持将列表作为参数。
0001 0000 0006 11 03 006B 0003是Modbus-TCP数据包的标准示例，其中包含：

0001: Transaction Identifier

0000: Protocol Identifier

0006: 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)

_Reference

因此，您可以使用上面的示例创建一个 Modbus-TCP 数据包：

import struct

transaction = 0x0001
identifier = 0x0000
length = 0x0006
unitid = 0x11
fcode = 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== H
identifier是2Byte ==短== H
length是2Byte ==短== H
unitid是1Byte == B
fcode是1Byte == B
reg_addr是2Byte ==短== H
count是2Byte ==短== H
B是unsigned byte
H是unsigned short

因此，格式将如下：>HHHBBHH

使用等效的pymodbus：

from pymodbus.client.sync import ModbusTcpClient

unitid = 0x11
fcode = 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.')

如何通过Modbus TCP发送“ struct.pack”类型的消息？

1 个答案:

使用等效的pymodbus：