參數(shù)資料
型號: QADCRM
英文描述: Queued Analog-to-Digital Converter Reference Manual
中文描述: 排隊模擬到數(shù)字轉(zhuǎn)換器參考手冊
文件頁數(shù): 52/122頁
文件大?。?/td> 940K
代理商: QADCRM
MOTOROLA
7-6
DIGITAL CONTROL
QADC
REFERENCE MANUAL
very short, software can momentarily read the status conditions, indicating that the
queue is paused. The trigger overrun flag is never set while in the software initiated
single-scan mode.
The software initiated single-scan mode is useful in the following applications:
Allows software complete control of the queue execution.
Allows the software to easily alternate between several queue sequences.
7.3.2.2 External Trigger Single-Scan Mode
The external trigger single-scan mode is a variation of the external trigger continuous-
scan mode, and is also available with both queue 1 and queue 2. The software pro-
grams the polarity of the external trigger edge that is to be detected, either a rising or
a falling edge. The software must enable the scan to occur by setting the single-scan
enable bit for the queue.
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 encountered. After the queue is completed, 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.
The external trigger single-scan mode is useful when the input trigger rate can exceed
the queue execution rate. Analog samples can be taken in sync with an external event,
even though the software is not interested in data taken from every edge. The software
can start the external trigger single-scan mode and get one set of data, and at a later
time, start the queue again for the next set of samples.
The external trigger single-scan mode is also useful when the software needs to
change the polarity of the external trigger so that both the rising and falling edges
cause queue execution.
7.3.2.3 Interval Timer Single-Scan Mode
Queue 2 can also use the periodic/interval timer in a single-scan queue operating
mode. The timer interval can range from 128 to 128K QCLK cycles in binary multiples.
When the interval timer single-scan mode is selected and the software sets the single-
scan enable bit in QACR2, the timer begins counting. When the time interval expires,
an internal trigger event is created 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 occurs, queue execution stops
until the timer interval expires again, and queue execution continues. When the queue
execution reaches an end of queue situation, 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.
F
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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