
MC68336/376
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
8-21
— Software can initiate the execution of a scan sequence for queue 1 or 2 by
selecting this mode, and setting the single-scan enable bit in QACR1 or
QACR2. A trigger event is generated internally and the QADC immediately
begins execution of the first CCW in the queue. If a pause is encountered,
queue execution ceases momentarily while another trigger event is generated
internally, and then execution continues. While the time to internally generate
and act on a trigger event is very short, software can momentarily read the sta-
tus conditions, indicating that the queue is paused.
— The QADC automatically performs the conversions in the queue until an end-
of-queue condition is encountered. The queue remains idle until software
again sets the single-scan enable bit. The trigger overrun flag is never set while
in this mode.
External trigger rising or falling edge single-scan mode
— This mode is a variation of the external trigger continuous-scan mode. It is
available for both queue 1 and queue 2. Software programs the external trigger
to be either a rising or a falling edge. Software must also set the single-scan
enable bit for the queue in order for the scan to take place. The first external
trigger edge causes the queue to be executed one time. Each CCW is read and
the indicated conversions are performed until an end-of-queue condition is en-
countered. After the queue scan is complete, the QADC clears the single-scan
enable bit. Software may set the single-scan enable bit again to allow another
scan of the queue to be initiated by the next external trigger edge.
Interval timer single-scan mode
— In addition to the above modes, queue 2 can also be programmed for the in-
terval timer single-scan mode. The queue operating mode for queue 2 is se-
lected by the MQ2 field in QACR2.
— When this mode is selected and software sets the single-scan enable bit in
QACR2, the periodic/interval timer begins counting. The timer interval can
range from 27 to 217 QCLK cycles in binary multiples. When the time interval
expires, a trigger event is generated internally to start the queue. The timer is
reloaded and begins counting again. Meanwhile, the QADC begins execution
with the first CCW in queue 2.
— The QADC automatically performs the conversions in the queue until a pause
or an end-of-queue condition is encountered. When a pause is encountered,
queue execution stops until the timer interval expires again; queue execution
then continues. When an end of queue condition is encountered, the timer is
held in reset and the single-scan enable bit is cleared.
— Software may set the single-scan enable bit again, allowing another scan of
the queue to be initiated by the interval timer. The interval timer generates a
trigger event whenever the time interval elapses. The trigger event may cause
queue execution to continue following a pause, or may be considered a trigger
overrun if the queue is currently executing.
8.12.3.3 Continuous-Scan Modes
When application software requires execution of multiple passes through a sequence
of conversions defined by a queue, a continuous-scan queue operating mode is
selected.