Rockwell Automation 1771-KA2 Communication Adapter Module - Manual (Page 74)

Command Initiation, Execution, and
Monitoring
Chapter 7
7-2
Figure 7.1 shows the timing of START and DONE bits for a command.
The significance of START/DONE bit status is summarized in Table 7.A.
Figure 7.1
START/DONE Bit Timing - Normal Operation
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A B C D
A
B
C
D
Start
Bit
On
Off
Done
Bit
On
Off
Command/
Response
Time
Processor
Scan Communication
Legend:
Start bit turned on by the program
Done bit set on by the 1771–KA2
communication adapter module to
indicate that a command has been completed.
Start bit turned off by the program
Done bit set off by the 1771–KA2
communication adapter module after
it senses that the start bit has been set off.
Adapter Scan
Table 7.A
START/DONE Bit Status
Status Significance
Start
Bit
Done
Bit
0 0 Idle
1 0 Command initiated or in progress
1 1 Command/reply operation complete
0 1 The processor, based on the program,
acknowledges completion of the
command/reply operation (transient condition,
since the communication adapter turns the
DONE bit OFF in its next scan.)