Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL - Manual (Page 57)

4–9 Planning an Application
Publication 2706-817
All messages, including Special Messages, must be triggered to be
displayed on, or used by, the MessageView terminal. A message may
be defined as only value trigger, or both value trigger and bit trigger.
•
Value trigger is acquired from either a logic controller or from an
ASCII Triggering Device.
•
Bit trigger is acquired only from a logic controller, using Remote
I/O communication.
Note: In time-critical or priority type applications, bit triggering is
recommended if available.
Important: An ASCII Triggering device cannot use Bit Triggering.
Value triggering
This method uses the message number as a trigger. Each message in
an application has its own unique number, so there are as many value
triggers in the application as there are messages.
When the terminal receives the message number value trigger, it
•
displays the message if its assigned lines are free and its Hidden
attribute is disabled
•
queues the message if its lines are occupied, the Hidden attribute
is disabled and the Message Queue is enabled
•
logs the message into the HE Stack whether is is displayed or not,
if its HE Stack attribute is enabled
•
ignores the message if the line(s) are occupied and the HE Stack
attribute and the Message Queue are disabled.
•
slaves the message whether displayed by the master device or not
if the slave attribute is enabled.
Some messages may be triggered but are not displayed:
•
messages with the Hidden attribute set
•
Special Messages.
Note: Any message that has its HE Stack or slave attribute set, is
sent to the Historic Event Stack or the slave device when it is
triggered. The message does not have to be displayed.
Triggering a Message