Rockwell Automation 2706 DL20 SERIES G USER MANUAL - Manual (Page 53)

Chapter 5
Run Mode
5–5
In this example, three messages are triggered in rapid succession. First, the
message 1 is triggered. The message queue looks like this:
First entry: 1
The entry is removed from the queue immediately. Message 1 is displayed.
While it is being displayed, a command to trigger message 2 is queued. The
message queue now looks like this:
First entry: 2
This entry is NOT removed, because message 1 is still being displayed and
its wait time has not elapsed. Next, a command to trigger message 3 is
received. The message queue now looks like this:
First entry: 2
Second entry: 3
After a short time, message 1 completes its display period. The DL20,
always working to empty the queue, removes the first entry from the queue, a
trigger for message 2. The message queue looks like this:
First entry: 3
When message 2 completes its display, the trigger for message 3 is removed.
The queue is now empty. The DL20s message 3 then waits indefinitely for
another message.
Display characteristics are determined by the attributes assigned to a
particular message. For example, if zero wait time is assigned to 3 messages
triggered in rapid succession, the first two messages are displayed too
quickly to be read. However, assigning a wait time to a message assures it is
displayed for the selected period of time. Other messages triggered during
this time are stacked in the queue.
The DL20 displays messages and data as a result of commands sent to it
from a host. Commands may be entered in one of two ways:
•
Parallel input consisting of twelve inputs (See Chapter 7)
•
Serial input using RS-232 or RS-422 port (See Chapter 6)
Important: Both serial and parallel inputs to the display cannot be used
simultaneously. One or the other must be used.
Queuing Examples
Transferring Data
to be Queued