Dynamic Chaining Example #2 - Allen-Bradley A-B QUALITY DL20 Series User Manual

Dynamic Chaining
Example #2
This example uses special message #8 and #9. This insures that the first
message triggered is the first displayed, and the remaining messages are also
displayed in the same order in which they are triggered. The messages are
continuously repeated in this order. Dynamic chaining mode must be
enabled.
Event 1: Under normal conditions (with dynamic chaining enabled) the
DL20 could be waiting for any fault or status message trigger.
Event 2: The operator attempts to start the system or machine, but several
fault conditions exist.
Event 3: The host controller sends the respective message triggers to the
DL20 as follows:
First special message #9 is triggered.
Then the message triggers that correspond to the faults are sent to the
DL20.
Next, special message #8 is sent to the DL20 so that the messages
can continuously be repeated.
Event 4: The operator corrects one or more of the fault conditions.
Event 5: If any change in a fault condition occurs, the host controller sends
an updated list of message triggers, as described in event 3.
Event 6: The operator again looks at the list of faults to see what else must
be done. Event 3 through 6 may be repeated until all faults have been
eliminated.
Event 7: When no more faults exist, the host controller triggers a message
that says NO FAULTS.
It is good practice to provide operators with a display messages button. This
enables the operator to refresh the DL20 while assuring the operator that
communications are functioning properly.
Chapter 5
Run Mode
5–15