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gate, TORn is set. This is considered an overrun condition. In this case, CF1 has been set
for the first end-of-queue condition and TORn sets for the second end-of-queue condition.
For TOR1 to set, CF2 must not be cleared before the second end-of-queue.
The QS field indicates the status of queue 1 and queue 2. Following are the five queue status
conditions:
• Idle
• Active
• Paused
• Suspended
• Trigger pending
The idle state occurs when a queue is disabled, when a queue is in a reserved mode, or when
a queue is in a valid queue operating mode awaiting a trigger event to initiate queue
execution. One or both queues may be in the idle state. When a queue is idle, CCWs are not
being executed for that queue, the queue is not in the pause state, and no trigger is pending.
A queue is in the active state when a valid queue operating mode is selected, when the
selected trigger event has occurred, or when the QADC is performing a conversion
specified by a CCW from that queue. Only one queue can be active at a time.
One or both queues can be in the paused state. A queue is paused when the previous CCW
executed from that queue had the pause bit set. The QADC does not execute any CCWs
from the paused queue until a trigger event occurs. Consequently, the QADC can service
queue 2 while queue 1 is paused.
Only queue 2 can be in the suspended state. When a trigger event occurs on queue 1 while
queue 2 is executing, the current queue 2 conversion is aborted and the queue 2 status is
reported as suspended. Queue 2 transitions back to the active state when queue 1 becomes
idle or paused.
A trigger pending state is required because both queues cannot be active at the same time.
The status of queue 2 is changed to trigger pending when a trigger event occurs for queue
2 while queue 1 is active. In the opposite case, when a trigger event occurs for queue 1 while
queue 2 is active, queue 2 is aborted and the status is reported as queue 1 active, queue 2
suspended. So due to the priority scheme, only queue 2 can be in the trigger pending state.
Two transition cases cause the queue 2 status to be trigger pending before queue 2 is shown
to be in the active state. When queue 1 is active and there is a trigger pending on queue 2,
after queue 1 completes or pauses, queue 2 continues to be in the trigger pending state for
a few clock cycles. The fleeting status conditions are:
• Queue 1 idle with queue 2 trigger pending
• Queue 1 paused with queue 2 trigger pending
Figure 27-12 displays the status conditions of the QS field as the QADC goes through the
transition from queue 1 active to queue 2 active.
MOTOROLA
Chapter 27. Queued Analog-to-Digital Converter (QADC)
Register Descriptions
27-21
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