National Instruments BridgeVIEW - Manual (Page 379)

Appendix A HMI Function Reference
© National Instruments Corporation A-59 BridgeVIEW User Manual
value is the latest value of the discrete tag read from the Real-Time
Database.
value timestamp returns the timestamp for when the tag value was last
updated.
error indicates that an error occurred when executing the Read Tag
(discrete) VI, or that the value output returned by Read Tag(discrete) is not
valid. See value status for the specific error condition.
shutdown indicates that the BridgeVIEW Engine is shutting down. In this
case, Read Tag (discrete) no longer waits for tags to be updated and returns
immediately with both timeout and shutdown TRUE. You can use
shutdown to exit any loop that uses Read Tag (discrete).
changed? is TRUE when Read Tag (discrete) returns a new value from the
Real-Time Database. If changed? is FALSE, Read Tag (discrete) probably
timed out before the tag value was updated.