Discipline I/Os are standardized combinations of inputs and outputs related to a specific application. They have a predefined number of parameters.
Three different input variable types can be interconnected to Discipline I/Os:
- Simple value
- Trigger value
- Commandable value
The input value can be connected via the data flow. In the engineering tool, this is preceded by a function block or compound, e.g., a Scheduler. However, if the input value is not connected, it can also be modified via BACnet client. The subsystem registers a change in the input value by comparing the value with the process image and transferring it to the field devices.
This input value is the logical image, or memory map, of an analog positioning command and describes its properties. Within the program, the Present Value is made available to the block as a program value. The block transfers the program value to the subsystem, from where it is transmitted to the field device.
Writing to this value acts as a trigger. This makes it possible, e.g., to generate the output of the same value (e.g., Lighting 100%, followed later by 100% again). In this case the subsystem registers the trigger value and transmits the value to the devices. This capability is required when the same variable can be modified from several sources (e.g., when Desigo CC writes 100.0%, the local operator unit writes 0.0% and the Desigo CC user wants to rewrite the value of 100.0%). The sources can be BACnet clients or system function blocks.
Only analog trigger values may be used.
The input value is the logical image, or memory map, of an analog positioning command and describes its properties. Within the program, the Present Value is made available to the block as a program value. The block transfers the program value to the subsystem, from where it is transmitted to the field device.
The commandable value is based on the BACnet priority-mechanism (which is the same as for the output blocks – refer to Section 0). A commandable value can be operated from various sources. Each source has its own priority. The sources are mutually exclusive (interlock). The source with the highest priority prevails, e.g., Emergency = Priority 1, Façade control = Priority 6, Operator = Priority = 8). The sources can be BACnet operator units or system function blocks (grouping function).
Only analog commandable values can be used.