Allen-Bradley A-B QUALITY DL20 Series User Manual page 154

Appendix G
Application Notes
PLC-2
Programming Examples
G–2
Triggering Simple Messages (PLC-2)
Figure G.1 illustrates how individual inputs can trigger corresponding
messages.
Figure G.1
Triggering Messages Using Individual Inputs (PLC-2)
057
G
001
112 060
G
00 020
112 061
G
01 021
112 062
G
02 022
If two or more inputs are true at the same time, the rung closest to the end of
the ladder diagram has priority and only this message is triggered during the
program scan.
When no inputs are true, the display clears since the 1st rung shown always
triggers special message #1 if none of the rungs after it are true. Special
message #1 clears the display. If your application requires that the last
message displayed remains displayed indefinitely, do not program the first
rung in this example. The DL20 Auto Clear message feature must be
disabled for this type of operation.
In this example, one rung is required for each unique message triggered.
The DL20 examines 10 bits (D0-D9) on the parallel port when a message
number is strobed in. If binary is selected, a range of message numbers
from 1 to 1022 is allowed. If BCD is selected, a range of message numbers
from 1 to 399 is allowed.
010
PUT Rung 1
001
010
PUT Rung 2
001
010
PUT Rung 3
001
010
PUT Rung 4
001