Motorola ColdFire MCF5281 - Manual (Page 557)

Queued Analog-to-Digital Converter (QADC)
Freescale Semiconductor 28-19
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 28-12 displays the status conditions of the QS field as the QADC goes through the transition from
queue 1 active to queue 2 active.
When a queue enters the paused state, CWP points to the CCW with the pause bit set. While in pause, the
CWP value is maintained until a trigger event occurs on either queue. Usually, the CWP is updated a few
clock cycles before the queue status field shows that the queue has become active. For example, a read of
CWP may point to a CCW in queue 2, while the queue status field shows queue 1 paused and queue 2
trigger pending.
When the QADC finishes a queue scan, the CWP points to the CCW where the end-of-queue condition
was detected. Therefore, when the end-of-queue condition is a CCW with the EOQ code (channel 63), the
CWP points to the CCW containing the EOQ.
When the last CCW in a queue is the last CCW table location (CCW63), and it does not contain the EOQ
code, the end-of-queue is detected when the following CCW is read, so the CWP points to word CCW0.
Finally, when queue 1 operation is terminated after a CCW is read that is pointed to by BQ2, the CWP
points to the same CCW as BQ2.
15 14 13 12 11 10 9 8
Field CF1 PF1 CF2 PF2 TOR1 TOR2 QS9 QS8
Reset 0000_0000
R/W: R/W R
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3