QADC
REFERENCE MANUAL
DIGITAL CONTROL
MOTOROLA
7-25
Only one queue can be active at a time. Either 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. 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 since 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.
There are two transition cases which 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 following are fleeting sta-
tus conditions:
Queue 1 idle with queue 2 trigger pending.
Queue 1 paused with queue 2 trigger pending.
Figure 7-4
displays the status conditions of the queue status field as the QADC goes
through the transition from queue 1 active to queue 2 active.
Figure 7-4 Queue Status Transition
The queue status field is affected by the stop mode. Since all of the analog logic and
control registers are reset, the queue status field is reset to queue 1 idle, queue 2 idle.
During the freeze mode, the queue status field is not modified. The queue status field
QUEUE 1
QUEUE 2
TRIGGER PENDING
TRIGGER PENDING
ACTIVE
IDLE
ACTIVE
ACTIVE
IDLE (PAUSED)
IDLE (PAUSED)
QADC QUEUE STATUS
F
Freescale Semiconductor, Inc.
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Go to: www.freescale.com
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