When objects are on scan

When an object is On Scan, the value and quality of the attribute configured with a Read/Write I/O Feature mirrors the quality of the externally referenced attribute during a successful read. The data quality of the attribute is set to Bad when reads fail. Reads can fail because of communication errors or datatype conversion failures.

While the object is On Scan, the data can change quality. If an external set (for example, from a user) to an attribute changes either the value or quality, then a write of the attribute’s value to the destination occurs during the next execute phase. The quality must be Good or Uncertain for a write to occur. For writes to occur because of a quality change, the quality change must be a transition from Bad or Initializing to Good or Uncertain.

The attribute called WriteValue is publicly exposed and plays an important role in driving outputs. When the object is Off Scan, quality is always Bad and user sets are accepted.