Motorola MPC533 Reference Manual page 551

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 QADC64E is performing a conversion
specified by a CCW from that queue.
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 QADC64E does not execute any CCWs from the paused queue until a trigger event
occurs. Consequently, the QADC64E 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 status conditions:
• Queue 1 idle with queue 2 trigger pending
• Queue 1 paused with queue 2 trigger pending
Figure 14-12 displays the status conditions of the queue status field as the QADC64E goes
through the transition from queue 1 active to queue 2 active.
MOTOROLAChapter 14. Queued Analog-to-Digital Converter Enhanced Mode Operation
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Queue 1
Active
Active
Idle (Paused)
Idle (Paused)
Figure 14-12. Queue Status Transition
Programming the QADC64E Registers
Queue 2
Idle
Trigger Pending
Trigger Pending
Active
QADC64E QUEUE STATUS
14-27