Usage

Dispatcher

Tolk is a JSON-RPC proxy for doing Modbus request over RTU or TCP. tolk.Dispatcher implements the JSON-RPC API. The tolk.Dispatcher needs a modbus_tk.modbus.Master to dispatch incoming requests to.

>>> import json
>>> from modbus_tk.modbus_tcp import TcpMaster
>>> from tolk import Dispatcher
>>> modbus_master = TcpMaster('localhost', 502)
>>> dispatcher = Dispatcher(modbus_master)
>>> dispatcher.call(json.dumps({
        'jsonrpc': '2.0',
        'method': 'read_holding_registers',
        'params': {
            'starting_address': 100,
            'quantity': 2,
        },
        'id': 1
    }
'{"jsonrpc": "2.0", "id": 1, "result": [1337, 2345]}'

Handler

tolk.Handler is a subclass of SocketServer.BaseRequestHandler. This class can delegate incomming JSON-RPC requests on a Unix Domain Socket or a TCP socket to an instance of tolk.Dispatcher.

from modbus_tk.modbus_tcp import TcpMaster
from SocketServer import UnixStreamServer

from tolk import Dispatcher, Handler

modbus_master = TcpMaster('localhost', 502)
dispatcher = Dispatcher(modbus_master)

server = UnixStreamServer('/tmp/tolk.sock', Handler)
# Bind the dispatcher on the server.
server.dispatcher = dispatcher

server.serve_forever()

Scripts

Tolk ships with 3 scripts to help during development and testing:

• modbus_tcp_slave.py: Create a Modbus slave listening at a port.
• tolk_server.py: Start Tolk server listening at Unix Domain Socket for JSON-RPC request to proxy to the Modbus slave.
• json_rpc_client.py: Send JSON-RPC requests to Tolk server.

Section Scripts tells more about these scripts.

Start the Modbus slave...:

$ ./scripts/modbus_tcp_slave --port=1025
[2015-10-03 11:02:47.796836] INFO: __main__: Add analog inputs data block from register 0 to 99 on slave 1
[2015-10-03 11:02:47.797037] INFO: __main__: Add discrete inputs data block from register 0 to 99 on slave 1
[2015-10-03 11:02:47.797176] INFO: __main__: Add coils data block from register 100 to 199 on slave 1
[2015-10-03 11:02:47.797305] INFO: __main__: Add holding registers block from register 100 to 199 on slave 1
[2015-10-03 11:02:47.797671] INFO: __main__: TcpServer started listening at port 1025.

...and the Tolk server...:

$ ./scripts/tolk_server.py --modbus-port=1025 --socket=/tmp/tolk.sock
[2015-10-03 11:04:05.661391] INFO: __main__: Start Tolk listening at /tmp/tolk.sock.

... and send requests:

$ ./scripts/json_rpc_client.py read_coils 100 1 --socket=/tmp/tolk.sock
{
    "id": 203448389051845515226734861262256644311,
    "jsonrpc": "2.0",
    "result": [
        0k
    ]
}