Rockwell Automation 2706-MB1 MESSAGEVIEW 421 SOFTWARE MANUAL - Manual (Page 56)

4–8 Planning an Application
Publication 2706-817
MessageView features supported by a logic controller
A MessageView terminal can support the following additional
features when controlled by a PLC or other logic controller:
•
supporting Handshaking for numeric entry and ACK messages as
well as for latched function keys
•
supporting bit triggering
•
supporting Startup and Background messages that contain
embedded display variables
•
sending Preset or Last values for variables to the controller
ASCII Triggering Device limitations:
•
If the ASCII network has more than one device, the terminal
operator must not send data (such as Entry variables embedded in
a message) from the MessageView terminal to the ASCII
Triggering device. This could cause data collisions. Consider this
when creating an application for such a network.
Data is sent from a terminal when:
– the ACK key is pressed (all terminals)
– numeric keys are used (421N and 421F terminals)
– an enabled Function key is pressed (421F terminals)
•
The MessageView terminal supports an output buffer to process
outgoing data responses. The buffer is designed to handle at least
two of the largest responses (such as 20 Ctrl-I responses or 2
messages that contain the maximum of 10 Entry Variables).
If the output buffer becomes full (for instance, if someone
repeatedly presses a Momentary Function Key before the data can
be sent), any new outgoing data is lost until the output buffer is
available again.
•
ASCII Trigger applications require a value trigger tag name to be
defined. See Page 10–21. Only the tag name is used; the node
address and node name may be left blank. The tag name is used
internally by the MessageView terminal as a reference.
Communication setup
In MessageBuilder software, a logic controller is specified by its
PLC/SLC/Scanner type. An ASCII Triggering device is a single
device that does not require a device type.