Digital Control Subsystem

Below the queue execution flows are three sets of blocks that show the status information that is made available to the user. The first two rows of status blocks show the condition of each queue as:

Idle

Active

Pause

Suspended (queue 2 only)

Trigger pending

The third row of status blocks shows the 4-bit QS status register field that encodes the condition of the two queues. Two transition status cases, QS = 0011 and QS = 0111, are not shown because they exist only very briefly between stable status conditions.

The first three examples in Figure 27-23through Figure 27-25(S1, S2, and S3) show what happens when a new trigger event is recognized before the queue has completed servicing the previous trigger event on the same queue.

In situation S1 (Figure 27-23), one trigger event is being recognized on each queue while that queue is still working on the previously recognized trigger event. The trigger overrun error status bit is set, and the premature trigger event is otherwise ignored. A trigger event that occurs before the servicing of the previous trigger event is through does not disturb the queue execution in progress.

Q1:

Q2:

QS:

 

 

T1

 

T1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q1:

 

C1

C2

 

C3

C4

 

T2

 

 

T2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TOR1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CF1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Q2:

C1

C2

 

C3

 

 

C4

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TOR2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CF2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IDLE

 

 

 

ACTIVE

 

 

 

 

 

 

 

 

IDLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

IDLE

 

 

 

 

 

 

 

ACTIVE

 

 

 

IDLE

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0000

 

1000

 

 

0000

 

0010

 

 

 

 

0000

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 27-23. CCW Priority Situation 1

In situation S2 (Figure 27-24), more than one trigger event is recognized before servicing of a previous trigger event is complete. The trigger overrun bit is again set, but the additional trigger events are otherwise ignored. After the queue is complete, the first newly detected trigger event causes queue execution to begin again. When the trigger event rate is high, a new trigger event can be seen very soon after completion of the previous queue,

MOTOROLA

Chapter 27. Queued Analog-to-Digital Converter (QADC)

27-41

Page 625
Image 625
Motorola MCF5281, MCF5282 user manual CCW Priority Situation