The Modbus Slave OPC Server supports communications to Modbus RTU and ASCII master applications. The OPC server supports the basic memory types and signal types for Modbus. The OPC Server supports multiple devices and multiple ports with one instance. The OPC server is multi-threaded for high-speed performance.
The setup of the OPC server is simple with a tag configuration that allows the user to define a point as a specific device address between 1-247, a memory type, an offset, and a signal type. These tags are defined under a port object. Multiple ports can be used at the same time if desired.
When the server is enabled for communications all tags will start with the OPC data quality of uncertain. When either on OPC client or a Modbus master sets the value of the tags the quality will go to good. If you wish to have the quality of the tags start with good quality set the parameter Start With Good Quality under Communications.
When the server receives a request for data on a port it will get the values for the first tags in the configuration that matches the request. If more than one tag has the same device address, memory type, and offset the value from the first tag in the configuration that matches the request will be passed back to the master. If the master sends a force or write data request the server will set all tags that match the same device address, memory type, and offset.
If the master queries for a device that is not defined under the port object no response will be provided. This will allow the OPC server to exist on a multi-drop network without interfering with communications with other devices. If the master requests multiple values and only some of the offsets exist in the configuration the non-existent offsets will be set with a value of 0. If the master sends a multiple or single offset force or set value and at least one tag with the correct device address, memory type, and offset is found a respond will be given. If no tag matches the set request no response will be given.
Features Include: