Rockwell Automation 1771-KA2 Communication Adapter Module - Manual (Page 75)

Command Initiation, Execution, and
Monitoring
Chapter 7
7-3
Faulty Operation
Certain fault conditions can prevent normal reception and execution of
commands by the receiving station. To indicate the source of such fault
conditions, the KA2 controls REMOTE and LOCAL FAULT bits at the
station processor.
In general, the LOCAL FAULT bit indicates that the local station cannot
confirm delivery of a command to the remote station. The REMOTE
FAULT bit, on the other hand, indicates that the intended receiving station
communication adapter module has received the command message, but
is unable to execute the command at its station processor. (For a quick
summary of the distinction between these FAULT types, refer to Figure
6.3.)
The timing relationship of these FAULT bits in command execution is
shown in Figure 7.2. In this example, the command initiated at the setting
of the START bit executed due to some fault condition. The
communication adapter module, detecting this fault condition, sets either
a LOCAL or REMOTE FAULT bit.
Figure 7.2
START/FAULT Bit Timing - Faulted Operation
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ЙЙЙЙЙЙЙЙЙЙЙЙЙЙЙ
ЙЙЙ
ЙЙЙ
ЙЙЙЙЙЙЙЙ
ЙЙЙЙЙЙЙЙ
ЙЙЙЙЙЙЙЙ
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A B C D
A
B
C
D
Start
Bit
On
Off
Remote or
Local Fault
Bit On
Off
On
Off Done
Bit
Command/
Response
Time Communication
Adapter Scan
Legend: Start bit turned on by the program
Remote fault or local bit set on
by the communication adapter module to
indicate that a fault condition has been detected.
Start bit turned off by program
Fault bit turned off by the communication
adapter module after it senses that start
bit has been turned off.