Table of Contents
Advertisement
The software also specifies whether the QADC64E is to perform a single pass through the
queue or is to scan continuously. When a single-scan mode is selected, the software selects
the queue operating mode and sets the single-scan enable bit. When a continuous-scan
mode is selected, the queue remains active in the selected queue operating mode after the
QADC64E completes each queue scan sequence.
During queue execution, the QADC64E reads each CCW from the active queue and
executes conversions in three stages:
• Initial sample
• Final sample
• Resolution
During initial sample, a buffered version of the selected input channel is connected to the
sample capacitor at the input of the sample buffer amplifier.
During the final sample period, the sample buffer amplifier is bypassed, and the multiplexer
input charges the sample capacitor directly. Each CCW specifies a final input sample time
of two or 16 QCLK cycles. When an analog-to-digital conversion is complete, the result is
written to the corresponding location in the result word table. The QADC64E continues to
sequentially execute each CCW in the queue until the end of the queue is detected or a
pause bit is found in a CCW.
When the pause bit is set in the current CCW, the QADC64E stops execution of the queue
until a new trigger event occurs. The pause status flag bit is set, which may cause an
interrupt to notify the software that the queue has reached the pause state. After the trigger
event occurs, the paused state ends and the QADC64E continues to execute each CCW in
the queue until another pause is encountered or the end of the queue is detected.
The following indicate the end-of-queue condition:
• The CCW channel field is programmed with 63 (0x3F) to specify the end of the
queue
• The end-of-queue 1 is implied by the beginning of queue 2, which is specified in the
BQ2 field in QACR2
• The physical end of the queue RAM space defines the end of either queue
When any of the end-of-queue conditions is recognized, a queue completion flag is set, and
if enabled, an interrupt is issued to the software. The following situations prematurely
terminate queue execution:
• Since queue 1 is higher in priority than queue 2, when a trigger event occurs on
queue 1 during queue 2 execution, the execution of queue 2 is suspended by aborting
the execution of the CCW in progress, and the queue 1 execution begins. When
queue 1 execution is completed, queue 2 conversions restart with the first CCW
entry in queue 2 or the first CCW of the queue 2 sub-queue being executed when
queue 2 was suspended. Alternately, conversions can restart with the aborted queue
MOTOROLAChapter 14. Queued Analog-to-Digital Converter Enhanced Mode Operation
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Programming the QADC64E Registers
14-31
Advertisement
Table of Contents
