I/O data quality

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

While the extended object is On Scan, it behaves as follows: If an external set (for example, from a user) to the configured attribute causes either the value or quality to change, then a write of the configured 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.

When the configured object is Off Scan, quality is always Bad and user sets are accepted.