Modbus Module¶

Configuration Example¶

Example section from configuration file:

<modbus name="outstation" mode="server">
    <endpoint>127.0.0.1:5502</endpoint>
    <register type="input">
        <address>30000</address>
        <tag>counter</tag>
    </register>
    <register type="input">
        <address>30001</address>
        <tag>bus-692.voltage</tag>
        <scaling>-2</scaling>
    </register>
    <register type="input">
        <address>30002</address>
        <tag>line-650632.kW</tag>
        <scaling>-2</scaling>
    </register>
    <register type="holding">
        <address>40000</address>
        <tag>reset</tag>
    </register>
    <register type="holding">
        <address>40001</address>
        <tag>line-650632.closed</tag>
    </register>
</modbus>

These configuration keys are described below.

Note

Please refer to the Modbus Organization for more information on the spec.

Modbus Module Overview¶

OT-sim supports four Modbus types (register type= above);

input — analog, read-only
holding — analog, read-write
discrete — binary, read-only
coil — binary, read-write

It is possible to configure 10,000 registers per type. In addition, the types input and holdings support scaling. Because Modbus only supports integers, scaling is used to "move the decimal" to the right or left.

- and an integer moves the decimal to the right
- For example, the value 98.6 on a server with scaling of -1 will send 986 to the client
+ and an integer moves the decimal to the left
- For example, the value 986 from a server with scaling of 1 on the client will result in 98.6 on the client

Note

scaling must be the same absolute value for both server and client configurations. On the server it should be negative and on the client it should be positive.

Note

When running as a Modbus client (<modbus mode="client">), a developer can provide the <period> element to configure how often the Modbus client queries the remote Modbus slave for updated values. If not provided, the period defaults to 5s.