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The choice of single-scan or continuous-scan applies to the full queue, and is not applied to
each subqueue. Once a subqueue is initiated, each CCW is executed sequentially until the
last CCW in the subqueue is executed and the pause state is entered. Execution can only
continue with the next CCW, which is the beginning of the next subqueue. A subqueue
cannot be executed a second time before the overall queue execution has been completed.
Conversion Command
Word (CCW) Table
P
00
0
Beginning of Queue 1
0
0
1
0
0
0
1
0
P
0
End of Queue 1
0
BQ2
0
Beginning of Queue 2
1
0
1
0
1
0
P
1
End of Queue 2
63
0
Trigger events which occur during the execution of a subqueue are ignored, but the trigger
overrun flag is set. When a continuous-scan mode is selected, a trigger event occurring after
the completion of the last subqueue (after the queue completion flag is set), causes the
execution to continue with the first subqueue, starting with the first CCW in the queue.
When the QADC encounters a CCW with the pause bit set, the queue enters the paused state
after completing the conversion specified in the CCW with the pause bit. The pause flag is
set in QASR0, and a pause interrupt may be requested. The status of the queue is shown to
be paused, indicating completion of a subqueue. The QADC then waits for another trigger
event to again begin execution of the next subqueue.
MOTOROLA
Pause
Pause
•
•
•
Pause
Pause
Pause
•
•
•
Pause
Figure 27-22. QADC Queue Operation with Pause
Chapter 27. Queued Analog-to-Digital Converter (QADC)
Channel Select,
Sample, Hold,
A/D Conversion
Digital Control Subsystem
Result Word Table
00
•
•
•
•
•
•
63
27-39
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