libmodbus の Python binding “pylibmodbus”1)を利用し、簡単に Modbus 機器と通信するプログラムを作ることができます。
ipython3 でインタラクティブに試すことができます。
実行例を下記に示します。
root@plum:~# ipython3
Python 3.4.3 (default, Oct 14 2015, 21:23:51)
Type "copyright", "credits" or "license" for more information.
IPython 1.2.1 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]: import pylibmodbus
In [2]: pylibmodbus.ModbusRtu?
Type: type
String Form:<class 'pylibmodbus.modbus_rtu.ModbusRtu'>
File: /usr/lib/python3/dist-packages/pylibmodbus/modbus_rtu.py
Docstring: <no docstring>
Constructor information:
Definition:pylibmodbus.ModbusRtu(self, device='/dev/ttyS0', baud=19200, parity='N', data_bit=8, stop_bit=1)
In [3]: rtu=pylibmodbus.ModbusRtu('/dev/ttyUSB0', baud=19200)
In [4]: rtu.connect()
In [5]: rtu.set_slave(1)
n [6]: rtu.read_input_bit(0)
Out[6]: 1
libmodbus の API Reference は、ここ にあります。
Python の API もほぼ同じ内容となっています。一部、使いやすいようメソッドを追加しています。
| Python | Arguments | libmodbus function | Note | |
|---|---|---|---|---|
| Context | ||||
| ModbusRtu | コンストラクタ | device=“/dev/ttyS0”, baud=19200, parity=“N”, data_bit=8, stop_bit=1 | modbus_new_rtu | Create a libmodbus context for RTU |
| Connection | ||||
| connect | modbus_connect | Establish a connection | ||
| clonse | modbus_close | Close a connection | ||
| Common | ||||
| set_slave | slave | modbus_set_slave | Set slave ID | |
| Client (Read data) | ||||
| read_bits | addr, nb | modbus_read_bits | Modbus function code 0x01 (read coil status) | |
| read_bit | addr | 〃 | ||
| read_input_bits | addr, nb | modbus_read_input_bits | Modbus function code 0x02 (read input status) | |
| read_input_bit | addr | 〃 | ||
| read_registers | addr, nb | modbus_read_registers | Modbus function code 0x03 (read holding registers) | |
| read_input_registers | addr, nb | modbus_read_input_registers | Modbus function code 0x04 (read input registers) | |
| Client (Write data) | ||||
| write_bit | addr, status | modbus_write_bit | Modbus function code 0x05 (force single coil) | |
| write_register | addr, value | modbus_write_register | Modbus function code 0x06 (preset single register) | |
| write_bits | addr, nb, data | modbus_write_bits | Modbus function code 0x0F (force multiple coils) | |
| write_registers | addr, data | modbus_write_registers | Modbus function code 0x10 (preset multiple registers) | |
| Client (Write and Read) | ||||
| write_and_read_registers | write_addr, data, read_addr, read_nb | modbus_write_and_read_registers | Modbus function code 0x17 (write/read registers) | |
| Timeout | ||||
| set_response_timeout | seconds | modbus_set_response_timeout | set the timeout interval used to wait for a response | |
| get_response_timeout | modbus_get_response_timeout | return the timeout interval used to wait for a response | ||