xtensive/dpa.ua.modbus

MODBUS OPC UA server implements MODBUS TCP protocol and exposes COIL, DI, HREG and IREG registers via OPC UA interface.

Command line arguments

--dev:<host[:port]>

MODBUS device ip and port (optionally), like "192.168.0.1" or "192.168.0.1:502".

--slave:<num>

Optional. MODBUS slave id.

--reconnectInterval:<num>

Optional. Reconnection interval between two consecutive connection atte***s, ms. Default is 5000 ms.

--requestInterval:<num>

Optional. Minimal interval between requests, ms. Default is 100 ms.

--responseTimeout:<num>

Optional. Timeout interval used to wait for a response, ms. Default is 1000 ms.

--byteTimeout:<num>

Optional. Timeout interval between two consecutive bytes of a message, ms. If there is no character in the buffer, the allowed timeout interval between two consecutive bytes is defined by byte timeout. Default is 1000 ms.

--readAtte***s:<num>

Optional. Maximal read atte***s before failure. Default is 3.

--instance:<str>

Optional. Specifies instance name for non-default instance. Instances are explained here.

--nocert

Optional. Do not use certificates. Indicates that OPC UA server should not expose secured endpoints.

How to run

The Docker container exposes TCP port 4840 for the OPC UA server.

docker run -p 4840:4840 xtensive/dpa.ua.modbus --dev:192.168.0.2 --slave:16 --reconnectInterval:3000 --nocert

To mount a volume for Instances, you can use the following command:

docker run -p 4840:4840 -v <local-path>:/dpa/instances xtensive/dpa.ua.modbus --dev:192.168.0.2 --slave:16

Address space

MODBUS OPC UA server provides [*] namespace which defines 4 variables to access COIL, DI, HREG and IREG registers respectively:

Objects/MODBUS/AS/COIL
Objects/MODBUS/AS/DI
Objects/MODBUS/AS/HREG
Objects/MODBUS/AS/IREG

Use OPC UA indexes to access particular register. For instance, to access HREG register number 32:

Objects/MODBUS/AS/HREG[32]

Ranges are supported as well. To read HREG values of registers 32-38:

Objects/MODBUS/AS/HREG[32:38]

To explicitly specify the slave number, use indexes with two components. For instance, to read HREG values of registers 32-38 from slave 13:

Objects/MODBUS/AS/HREG[13,32:38]

Aliases are human-readable shortcuts, allowing easy access to indexed registers using clear notations such as "temperature", "speed", etc. Conversion and data transformation are also supported. For example, to convert two 16-bit registers into one value of type "float".

Troubleshooting

Server fails to start

All diagnostic messages are sent to stdout and stderr. For instance, when OPC UA server fails to read the certificate or the private key:

[2023-10-18 11:07:13.019 (UTC+0300)] fatal/server       Could not load certificate storage.

In that case ensure that .cert and .key files exist and are located according to Instances directory structure.

An invalid or corrupted alias.json file may cause service to fail to start:

[2023-10-18 11:08:54.418 (UTC+0300)] fatal/server       Could not load alias json.

In that case ensure that alias.json is valid and its content respects the demands described here. Take into account that e***y alias.json file is ***ed as invalid. If aliases are not used, just remove alias.json.

License

If the license is not installed or if the license is not valid, for example, an expired TRIAL license, then the OPC UA server will function for 1 hour after starting the process. After the hour has elapsed, the OPC UA server will return a BADLICENSENOTAVAILABLE or BADLICENSEEXPIRED error on requests to read and write data, except for system objects and system variables of OPC UA server.

The variable "Objects/Server/Instance/LicenseKey" allows to read the loaded license and its status. Next, the license status can be checked with the command line utility dpa.opcua.rs:

dpa.opcua.rs.exe target <OpcServerIp>

MODBUS communication

To troubleshoot any MODBUS communication issues, please, refer to "Objects/MODBUS/link" variable. It provides detailed information about the status of MODBUS TCP connection as well as any errors detected, including the rich set of counters for various types of errors.