National Instruments BridgeVIEW - Manual (Page 124)

Chapter 4 Human Machine Interface
BridgeVIEW User Manual 4-20 © National Instruments Corporation
Tag constants in your diagram (and tag controls and indicators if they are
saved with default values) retain the tag name or tag group name selected
when your VI is saved. The name contained in the tag control, indicator
or constant is dimmed when the name is not contained in the currently
selected
.scf file. This might be because the tag name has been deleted
from the .scf file, or the VI was created using a different .scf file. If you
try to run the VI at this point, you will get a system error for each tag that
is undefined in the current
.scf file. You can control which .scf file the
BridgeVIEW Engine runs programmatically. This capability is covered in
Chapter 7,
Advanced Application Topics .
Tags VIs and Alarms and Events VIs
The Tags VIs and Alarms and Events VIs have several properties in
common. With these VIs, you operate on tags by wiring the tag name or tag
group name into the tag name or group/tag name input of the VI when
you place them in your diagram. These are required inputs. Some VIs
accept arrays of tag names or tag and tag group names.
The Tags VIs and Alarms and Events VIs return several flags that indicate
the state of the BridgeVIEW Engine. They return a Boolean error flag to
indicate whether the operation was successful. If the error flag is TRUE,
the tag specific information returned by the VI might not be valid. Some
VIs also return a more detailed value status variable.
All the VIs return a shutdown indication. If TRUE, this output indicates
that the BridgeVIEW Engine is in the shutdown state, and your application
must finish execution so that shutdown can finish. If the BridgeVIEW
Engine goes into the shutdown state while these VIs are waiting on an
event, the VI terminates the wait and returns immediately to the calling
diagram. You can use this output to tell your diagram to complete
execution.
All VIs that read information from the BridgeVIEW database can return
information immediately or wait for the database to be updated with new
information before returning. The timeout input controls this behavior.
This input tells the VI how long to wait, in seconds, for the tag information
to be updated in the Real-Time Database.
If timeout is 0 seconds, the VI immediately reads the database and returns
the current tag information. If timeout is less than 0, the VI continues to
wait until the tag is updated or the Engine shuts down. If timeout is greater
than 0, the VI waits until the tag is updated in the database, or the timeout