MC68336/376
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
8-20
The pause bit is set in CCW0A and EOQ is programmed into CCW0A.
During queue 1 operation, the pause bit is set in CCW20, which is also BQ2.
8.12.3 Scan Modes
The QADC queuing mechanism provides several methods for automatically scanning
input channels. In single-scan mode, a single pass through a sequence of conversions
defined by a queue is performed. In continuous-scan mode, multiple passes through
a sequence of conversions defined by a queue are executed. The following para-
graphs describe the disabled/reserved, single-scan, and continuous-scan operations.
8.12.3.1 Disabled Mode and Reserved Mode
When the disabled mode or a reserved mode is selected, the queue is not active.
NOTE
Do not use a reserved mode. Unspecified operations may result.
Trigger events cannot initiate queue execution. When both queue 1 and queue 2 are
disabled, no wait states will be inserted by the QADC for accesses to the CCW and
result word tables. When both queues are disabled, it is safe to change the QADC
clock prescaler values.
8.12.3.2 Single-Scan Modes
When application software requires execution of a single pass through a sequence of
conversions defined by a queue, a single-scan queue operating mode is selected.
In all single-scan queue operating modes, software must enable a queue for execution
by writing the single-scan enable bit to one in the queue’s control register. The single-
scan enable bits, SSE1 and SSE2, are provided for queue 1 and queue 2,
respectively.
Until the single-scan enable bit is set, any trigger events for that queue are ignored.
The single-scan enable bit may be set to one during the write cycle that selects the
single-scan queue operating mode. The single-scan enable bit can be written as a one
or a zero but is always read as a zero.
After the single-scan enable bit is set, a trigger event causes the QADC to begin exe-
cution with the first CCW in the queue. The single-scan enable bit remains set until the
queue scan is complete; the QADC then clears the single-scan enable bit to zero. If
the single-scan enable bit is written to one or zero before the queue scan is complete,
the queue is not affected. However, if software changes the queue operating mode,
the new queue operating mode and the value of the single-scan enable bit are recog-
nized immediately. The current conversion is aborted and the new queue operating
mode takes effect.
By properly programming the MQ1 field in QACR1 or the MQ2 field in QACR2, the fol-
lowing modes can be selected for queue 1 and/or 2:
Software initiated single-scan mode