Digital Control Subsystem

27.8.1 Queue Priority Timing Examples

This subsection describes the QADC priority scheme when trigger events on two queues overlap or conflict.

27.8.1.1Queue Priority

Queue 1 has priority over queue 2 execution. These cases show the conditions under which queue 1 asserts its priority:

When a queue is not active, a trigger event for queue 1 or queue 2 causes the corresponding queue execution to begin.

When queue 1 is active and a trigger event occurs for queue 2, queue 2 cannot begin execution until queue 1 reaches completion or the paused state. The status register records the trigger event by reporting the queue 2 status as trigger pending.

Additional trigger events for queue 2, which occur before execution can begin, are flagged as trigger overruns.

When queue 2 is active and a trigger event occurs for queue 1, the current queue 2 conversion is aborted. The status register reports the queue 2 status as suspended. Any trigger events occurring for queue 2 while it is suspended are flagged as trigger overruns. Once queue 1 reaches the completion or the paused state, queue 2 begins executing again. The programming of the RESUME bit in QACR2 determines which CCW is executed in queue 2.

When simultaneous trigger events occur for queue 1 and queue 2, queue 1 begins execution and the queue 2 status is changed to trigger pending.

When subqueues are paused

The pause feature can be used to divide queue 1 and/or queue 2 into multiple subqueues. A subqueue is defined by setting the pause bit in the last CCW of the subqueue.

Figure 27-22shows the CCW format and an example of using pause to create subqueues. Queue 1 is shown with four CCWs in each subqueue and queue 2 has two CCWs in each subqueue.

The operating mode selected for queue 1 determines what type of trigger event causes the execution of each of the subqueues within queue 1. Similarly, the operating mode for queue 2 determines the type of trigger event required to execute each of the subqueues within queue 2.

For example, when the external trigger rising edge continuous-scan mode is selected for queue 1, and there are six subqueues within queue 1, a separate rising edge is required on the external trigger signal after every pause to begin the execution of each subqueue (refer to Figure 27-22).

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MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282, MCF5281 user manual Queue Priority Timing Examples