Motorola MCF5281, MCF5282 user manual Queued Analog-to-Digital Converter Qadc 27-21

Register Descriptions

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 27-12displays 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) 27-21