Print(" The modbus slave connected but exception code returned: %d." % coil_response.exception_code)Ĭoil_response = client.read_coils(address=ADDRESS_START, count=1, unit=DEVICE_ID) ".format(ADDRESS_START))Ĭoil_response = client.write_coil(address=ADDRESS_START, value=rand_value, unit=DEVICE_ID) # client.read_coils(address, count, unit)Ĭoil_response = client.read_coils(address=ADDRESS_START, count=ADDRESS_LENGTH, unit=DEVICE_ID) # the unit is the device ID Print(" Fail to connect to modbus slave %s:%d." % (SERVER_IP, SERVER_PORT)) connect() returns True if connection established SERVER_IP = 'localhost' # aka modbus slaveĬlient = ModbusTcpClient(host=SERVER_IP, port=SERVER_PORT) Only availabel if `.isError()` returns true. `.registers`: A list of reading result. `unit`: The slave unit(device ID) this request is targeting `count`: The number of registers to read You should read it with relative address by removing leading `4` and ubstract by `1`. For example, an address `400001` on a PLC manual is belong to AI. `address`: The starting address to read from. | `.read_input_registers()` | (AO)Holding Register |įour read funcions listed above have same parameters: | `.read_holding_registers()` | (AI)Input Register | | `.read_discrete_inputs()` | (DI)Input Status | Res.registers # shows the result, type: list Res = client.read_holding_registers(address=0, count=2, unit=1) # Once it's connected, this function always returns true even the physical connection is dead.Ĭnnect() # returns True if connection established `strict`: Use Inter char timeout for baudrates <= 19200 (adhere to modbus standards) ![]() `timeout`: The timeout between serial requests (default 3s) `baudrate`: The baud rate to use for the serial device `bytesize`: The bytesize of the serial messages `stopbits`: The number of stop bits to use `method`: The method to use for connection (`ascii`, `rtu`, `binary`) | 11, 0x0B | gatewat target no response | |įrom import ModbusTcpClientĬlient = ModbusTcpClient(host='192.168.87.87', port=123)įrom import ModbusSerialClientĬlient = ModbusSerialClient(method='rtu', port='COM8') | 10, 0x0A | gateway path unavailable | | | 05 | acknowledge | The requests is accepted, but the slave requires much time to finish the task. | Exception code | Represents | Description | When a modbus master(client) send a unexpected requests to the modbus slave(server), the slave would return the request with exception code. | 22 (0x16) | Write multiple AO(Up to 120 contiguous words) | | 16 (0x10) | Write multiple DO(Up to 1968 contiguous bits) | | 04 (0x04) | Read AI(Up to 125 contiguous words) | | 03 (0x03) | Read AO(Up to 125 contiguous words) | | 02 (0x02) | Read DI(Up to 2000 contiguous bits) | | 01 (0x01) | Read DO(Up to 2000 contiguous bits) | The library `pymodbus` already handles the function code of modbus well, but it's good to know there is such a thing in case you may have to sniff the packages for debugging. > You have to specify a modbus point type when accessing data by PDU address, which is the case of functions of pymodbus. > For AI and AO, each register is 1 word = 16 bits = 2 bytes. | AO(Holding Register) | 400001 | 0~65535 | unsigned word(2 bytes) | Read/Write | | AI(Input Register) | 300001 | 0~65535 | unsigned word(2 bytes) | Read only | | Modbus point type | Absolute Address | PDU Address | Data type | Master Access | However, in most applications, PDU addresses are no bigger then 1000, and the absolute addresses are denoted as 00001, 10001, 3001. Note that the table below shows the maximum range defined by (). You can use a simlation software as an modbus slave, see (). ![]() It's okay that you don't have a modbus slave device, such as PLC. You can also visit () for more information. This note is written with `pymodbus=2.3.0`. ![]() Hence I can not understand well the usage from the (), here is the note for pymodbus. Tags: notes, RT_blog, python, modbus, pymodbus
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