Rockwell Automation 1771-KA2 Communication Adapter Module - Manual (Page 78)

Command Initiation, Execution, and
Monitoring
Chapter 7
7-6
Figure 7.3
Status-Initiated Command
L
032 12 11111 03312
/
03302
/
03302
U
032 03202 11111
/
Remote
Fault Local
Fault
Input
Local
03312
Remote
Input Done Start
Start
Fault
Fault
12
In this example, the first rung is programmed to LATCH the START bit
when the input, bit 11111, is ON, provided that both FAULT bits are OFF.
The second rung is programmed to UNLATCH the START bit based on
the response of the communication adapter module.
In normal operation, the START bit is LATCHED by the input 11111; the
FAULT bits, initially, are OFF. This causes the command message to be
formatted and sent. Then, when the command is completed, the DONE
bit is set ON by the communication adapter module. Note that the input
bit, 11111, must also be OFF to UNLATCH the START bit in this
example. With this arrangement, the command message is sent only once;
input 11111 must be turned OFF, then ON again, to execute this command
a second time. In normal operation, the START bit, after successful
command completion, remains ON until input 11111 goes OFF. (Recall
from Figure 7.1 that the communication adapter module holds the DONE
bit ON until after the START bit is turned OFF.)
Should a fault condition prevent normal execution, these rungs provide a
programmed re-try of the command. A REMOTE or LOCAL FAULT bit
resets the START bit in the second rung. In the first rung, the START bit
is LATCHED again after the communication adapter module resets the
FAULT bit. (As Figure 7.2 shows, the 1771-KA2 module resets a FAULT
bit only after the START bit has been turned OFF.)