Motorola MCF5282 ユーザーズマニュアル
27-40
MCF5282 User’s Manual
MOTOROLA
Digital Control Subsystem
27.8.1.2 Queue Priority Schemes
Because there are two conversion command queues and only one A/D converter, a priority
scheme determines which conversion occurs. Each queue has a variety of trigger events that
are intended to initiate conversions, and they can occur asynchronously in relation to each
other and other conversions in progress. For example, a queue can be idle awaiting a trigger
event; a trigger event can have occurred, but the first conversion has not started; a
conversion can be in progress; a pause condition can exist awaiting another trigger event to
continue the queue; and so on.
scheme determines which conversion occurs. Each queue has a variety of trigger events that
are intended to initiate conversions, and they can occur asynchronously in relation to each
other and other conversions in progress. For example, a queue can be idle awaiting a trigger
event; a trigger event can have occurred, but the first conversion has not started; a
conversion can be in progress; a pause condition can exist awaiting another trigger event to
continue the queue; and so on.
The following paragraphs and figures outline the prioritizing criteria used to determine
which conversion occurs in each overlap situation.
which conversion occurs in each overlap situation.
NOTE
Each situation in Figure 27-23 through Figure 27-33 is labeled
S1 through S19. In each diagram, time is shown increasing
from left to right. The execution of queue 1 and queue 2 (Q1
and Q2) is shown as a string of rectangles representing the
execution time of each CCW in the queue. In most of the
situations, there are four CCWs (labeled C1 to C4) in both
queue 1 and queue 2. In some of the situations, CCW C2 is
presumed to have the pause bit set, to show the similarities of
pause and end-of-queue as terminations of queue execution.
S1 through S19. In each diagram, time is shown increasing
from left to right. The execution of queue 1 and queue 2 (Q1
and Q2) is shown as a string of rectangles representing the
execution time of each CCW in the queue. In most of the
situations, there are four CCWs (labeled C1 to C4) in both
queue 1 and queue 2. In some of the situations, CCW C2 is
presumed to have the pause bit set, to show the similarities of
pause and end-of-queue as terminations of queue execution.
Trigger events are described in Table 27-22.
When a trigger event causes a CCW execution in progress to be aborted, the aborted
conversion is shown as a ragged end of a shortened CCW rectangle.
conversion is shown as a ragged end of a shortened CCW rectangle.
The situation diagrams also show when key status bits are set.
Table 27-23 describes the status bits.
Table 27-23 describes the status bits.
Table 27-22. Trigger Events
Trigger
Events
T1
Events that trigger queue 1 execution (external trigger, software-initiated single-scan enable
bit, or completion of the previous continuous loop)
bit, or completion of the previous continuous loop)
T2
Events that trigger queue 2 execution (external trigger, software-initiated single-scan enable
bit, timer period/interval expired, or completion of the previous continuous loop)
bit, timer period/interval expired, or completion of the previous continuous loop)
Table 27-23. Status Bits
Bit
Function
CF flag
Set when the end of the queue is reached
PF flag
Set when a queue completes execution up through a pause bit
Trigger overrun
error (TOR)
Set when a new trigger event occurs before the queue is finished servicing the
previous trigger event
previous trigger event