Specifications

RSLinx – Training Guide A - 15
Show Last Acquired Value in Graphics:
By default graphic screens have this property checked or enabled. The last
acquired value is displayed on a graphic, rather than a wireframe outline
indicating the data is not fresh, when this property is enabled. The last acquired
value is never displayed when the tag is in Error.
For more information on Tag states:
Jump to A202 - Tag State Information
This property is intended to show the user the last POLLED value, for data that is
slow to update, such as a dialup modem network. Remember when the screen is
closed all data important to that screen is no longer needed, and is removed
from the Active Items list in RSLinx. The next time the screen is displayed, the
data is initially read. The Show Last Acquired Value screen setting is intended to
present the last value read while waiting for the new value to be read.
If an unsolicited write comes in while the screen is closed, then RSLinx has no
place to send the data, so it is lost. RSLinx does not buffer this data. The next
time the screen is displayed the data is stale or uninitialized and appears to be
wire framed on the graphic display regardless of the setting of Show Last
Acquired Value. If however, the topic in RSLinx has been configured to be polled
as well as accept unsolicited data, then each time the screen is displayed, the
data will be read. The object remains wireframed until the read is complete.
For more information on how to successfully implement unsolicited / polled data
in the HMI:
Jump to A449 Receiving Unsolicited Messages in RSView32 with RSLinx
One exception to this active items list rule is when the Display Setting Cache
After Displaying is set to Yes, and the Always Updating option is checked. This
forces all screen data to be continually polled. Other exceptions are when the
data is also being used in a background task such as Datalog, Alarming, Events,
Derived tags or a tag object has been Dim'ed WithEvents in VB or VBA.
Whenever a task requires the data then it remains on the Active Items list in
RSLinx even when the graphic is closed.
Once RSView32 accesses data associated with a topic, that topic becomes
locked in RSLinx. A locked topic can't be modified, except the poll rate can be
changed. The topic remains locked even after the graphic is closed, or the
project is stopped. To unlock a topic the project must be closed. Topics remain
locked after a graphic screen is closed or the project is stopped for performance
optimization.