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

NOTE

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.

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MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282, MCF5281 user manual Continuous-Scan Modes