Appendix A
HMI Function Reference
A-60
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National Instruments Corporation
Read Tag (string)
Use the Read Tag (string) VI to read the latest value for the tag from the Real-Time Database.
If timeout is 0, Read Tag (string) VI returns the current Tag value and update timestamp from
the Real-Time Database, otherwise the Read Tag (string) VI waits up to the specified timeout
for the tag to be updated in the Real-Time Database, and returns the new value.
Note
Use a separate Read Tag (string) VI for each tag you want to monitor. Do not put
the Read Tag (string) VI in a loop to read a different tag each iteration of the loop.
This results in slower program performance. The Read Tag(string) VI is designed
to save information about the tag internally for efficient operation. This
information is updated every time the tag name changes.
tag name is the name of the tag.
timeout (secs) (0) specifies how many seconds to wait for the tag value to
be updated in the Real-Time Database before reading the Real-Time
Database for the latest value. If timeout is the default value of 0, the Read
Tag (string) VI reads the Real-Time Database immediately and returns the
tag value without waiting. If timeout is –1, Read Tag (string) waits
indefinitely until the tag value is updated, or the Real-Time Database shuts
down, whichever occurs first. If a timeout occurs before the value is
updated, Read Tag (string) returns the most recent value from the
Real-Time Database, and timeout is set to TRUE.
in alarm is TRUE if the tag is in alarm.
value status returns the status of the value. If value status is greater than
or equal to 0, the value returned by Read Tag is valid and there is a warning
about the tag value. If value status is less than 0, either the device server
has reported an error indicating there is a problem with the tag, or
BridgeVIEW has reported an error indicating there is a problem using
the tag.
value is the latest value of the tag read from the Real-Time Database.
