MC68F375
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
MOTOROLA
REFERENCE MANUAL
Rev. 25 June 03
5-15
table. A queue is a scan sequence of one or more input channels. By using a pause
mechanism, subqueues can be created within the two queues. Each queue can be
operated using several different scan modes. The scan modes for queue 1 and queue
2 are programmed in QACR1 and QACR2. Once a queue has been started by a trigger
event (any of the ways to cause the QADC64 to begin executing the CCWs in a queue
or subqueue), the QADC64 performs a sequence of conversions and places the
results in the result word table.
5.10.1 Queue Priority
Queue 1 has execution priority over queue 2 execution. Table 5-3 shows the condi-
tions under which queue 1 asserts its priority:
Figure 5-7 shows the CCW format and an example of using pause to create sub-
queues. Queue 1 is shown with four CCWs in each subqueue and queue 2 has two
CCWs in each subqueue.
Table 5-3 Queue 1 Priority Assertion
Queue State
Result
Inactive
A trigger event for queue 1 or queue 2 causes the corresponding queue execution to
begin.
Queue 1 active/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 recorded as trigger overruns.
Queue 2 active/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 queue 2 is sus-
pended are recorded 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.
Simultaneous trigger events
occur for queue 1 and queue 2
Queue 1 begins execution and the queue 2 status is changed to trigger pending.
Subqueues paused
The pause feature can be used to divide queue 1 and/or queue 2 into multiple sub-
queues. A subqueue is defined by setting the pause bit in the last CCW of the sub-
queue.
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Freescale Semiconductor, Inc.
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