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Digital Control Subsystem
• When the interrupt rate in the periodic timer continuous-scan mode would be too
high
• In sensitive battery applications, where the interval timer single-scan mode uses less
power than the software-initiated continuous-scan mode
27.8.7 Continuous-Scan Modes
A continuous-scan queue operating mode is used to execute multiple passes through a
sequence of conversions defined by a queue. By programming the MQ1 field in QACR1 or
the MQ2 field in QACR2, these modes can be selected:
• Software-initiated continuous-scan mode
• Externally triggered continuous-scan mode
• Externally gated continuous-scan mode
• Periodic timer continuous-scan mode
Queue 2 cannot be programmed for externally gated
continuous-scan mode.
When a queue is programmed for a continuous-scan mode, the single-scan enable bit in the
queue control register does not have any meaning or effect. As soon as the queue operating
mode is programmed, the selected trigger event can initiate queue execution.
In the case of software-initiated continuous-scan mode, the trigger event is generated
internally and queue execution begins immediately. In the other continuous-scan queue
operating modes, the selected trigger event must occur before the queue can start. A trigger
overrun is captured if a trigger event occurs during queue execution in the externally
triggered continuous-scan mode or the periodic timer continuous-scan mode.
After queue execution is complete, the queue status is shown as idle. Because the
continuous-scan queue operating modes allow the entire queue to be scanned multiple
times, software involvement is not needed for queue execution to continue from the idle
state. The next trigger event causes queue execution to begin again, starting with the first
CCW in the queue.
27-54
NOTE
MCF5282 User's Manual
MOTOROLA
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