VTScada applications that are based on Data Flow RTUs use a slightly different tag configuration than those based on other RTUs or PLCs. Systems that are based on hardware other than Data Flow RTUs require polling driver tags if you want to be able to switch between fast scans of the real equipment driver and infrequent polling on demand.
The tag hierarchies for Data Flow-based systems and systems based on other hardware are described below.
For both types of systems, a serial port tag opens a port on the PC through which data is transmitted and received. The port number to be used by your application can be set using the serial port tag’s Port Number property on the Settings tab of the serial port tag’s properties folder. Many communication drivers can refer to a single serial port tag.
Systems Based on Non-Data Flow RTUs or PLCs
A communication driver tag (according to the type of hardware with which your application is interfacing) is associated with the serial port tag by means of its Port property (typically on the Serial tab of the tag properties folder). There must be one communication driver tag configured for each PLC or RTU in your system.
A polling driver tag is associated with a communication driver tag by means of its I/O Device property on the I/O tab of the polling driver tag’s properties folder. There must be one polling driver tag configured per communication driver tag in your application.
Input and output tags are associated with a polling driver tag by means of the I/O Device or Site property on the I/O tab of the input or output tag’s properties folder. There may be any number of input and output tags associated with a given polling driver tag.
System Based on Data Flow RTUs
A Data Flow RTU tag is associated with the serial port tag by means of its Serial Port Tag Name property on the I/O tab of the tag properties folder. There must be one Data Flow RTU driver tag configured for each Data Flow RTU in your system.
Input and output tags are associated with a Data Flow RTU driver tag by means of the I/O Device or Site property on the I/O tab of the input or output tag’s properties folder. There may be any number of input and output tags associated with a given Data Flow RTU driver tag.