MMC2107 - Freescale Semiconductor

Freescale Semiconductor, Inc.
Queued Analog-to-Digital Converter (QADC)
Digital Control
18.10.7.1 Software-Initiated Continuous-Scan Mode
When the software-initiated continuous-scan mode is programmed, the
trigger event is generated automatically by the QADC. Queue execution
begins immediately. If a pause is encountered, another trigger event is
generated internally, and then execution continues without pausing.
When the end-of-queue is reached, another internal trigger event is
generated and queue execution begins again from the beginning of the
queue.
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While the time to internally generate and act on a trigger event is very
short, software can momentarily read the status conditions, indicating
that the queue is idle. The trigger overrun flag is never set while in the
software-initiated continuous-scan mode.
The software-initiated continuous-scan mode keeps the result registers
updated more frequently than any of the other queue operating modes.
The software can always read the result table to get the latest converted
value for each channel. The channels scanned are kept up to date by the
QADC without software involvement. Software can read a result value at
any time.
The software-initiated continuous-scan mode may be chosen for either
queue, but is normally used only with queue 2. When the
software-initiated continuous-scan mode is chosen for queue 1, that
queue operates continuously and queue 2, being lower in priority, never
gets executed. The short interval of time between a queue 1 completion
and the subsequent trigger event is not sufficient to allow queue 2
execution to begin.
The software-initiated continuous-scan mode is a useful choice with
queue 2 for converting channels that do not need to be synchronized to
anything, or for the slow-to-change analog channels. Interrupts are
normally not used with the software-initiated continuous-scan mode.
Rather, the software reads the latest conversion result from the result
table at any time. Once initiated, software action is not needed to sustain
conversions of channel.
MMC2107 – Rev. 2.0
Technical Data
MOTOROLA Queued Analog-to-Digital Converter (QADC) 473
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