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Register Descriptions
• When the current CCW contains the end-of-queue code (channel 63) instead of a
valid channel number
• When the currently completed CCW is in the last location of the CCW RAM.
Once PFn is set, the queue enters the paused state and waits for a trigger event to allow
queue execution to continue. However, a special case occurs when the CCW with the pause
bit set is the last CCW in a queue; queue execution is complete. The queue status becomes
idle, not paused, and both the pause and completion flags are set.
Another special case occurs when the queue is operating in software-initiated single-scan
or continuous-scan mode and a CCW pause bit is set. The QADC will set PFn and will also
automatically generate a retrigger event that restarts execution after two QCLK cycles.
Pause mode is never entered.
In externally gated single-scan and continuous-scan mode, the behavior of PFn has been
redefined. When the gate closes before the end of the queue is reached, PFn is set to indicate
that an incomplete scan has occurred. In single-scan mode, a resultant interrupt can be used
to determine if the queue should be enabled again. In either externally gated mode, setting
PFn indicates that the results for the queue have not been collected during one scan
(coherently).
If a set CCW pause bit is encountered in either externally gated
mode, the pause flag will not set, and execution continues
without pausing. This has allowed for the modified behavior of
PF1 in the externally gated modes.
PFn is maintained by the QADC regardless of whether the
corresponding interrupt is enabled. PFn may be polled to
determine if the QADC has reached a pause in scanning a
queue.
A trigger event generated by a transition on the external trigger signal or by the
periodic/interval timer may be captured as a trigger overrun. TORn cannot be set when the
software-initiated single-scan mode or the software-initiated continuous-scan mode is
selected.
TORn is set when a trigger event is received while a queue is executing and before the scan
has completed or paused. TORn has no effect on queue execution.
After a trigger event has occurred for queue 1, and before the scan has completed or paused,
additional queue 1 trigger events are not retained. Such trigger events are considered
unexpected, and the QADC sets the TORn error status bit. An unexpected trigger event may
denote a system overrun situation.
In externally gated continuous-scan mode, the behavior of TORn has been redefined. In the
case that the queue reaches an end-of-queue condition for the second time during an open
27-20
NOTE:
MCF5282 User's Manual
MOTOROLA
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