MMC2114 MOTOROLA [Motorola, Inc], MMC2114 Datasheet - Page 500

• Manufacturer Part Number: MMC2114
• Description: M CORE Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Queued Analog-to-Digital Converter (QADC)
19.10.7.1 Software-Initiated Continuous-Scan Mode
Advance Information
500
between the last queue conversion and the first queue conversion
requires one additional CCW fetch cycle. Continuous samples are not
coherent at this boundary.
In addition, the time from trigger to first conversion cannot be
guaranteed, because it is a function of clock synchronization,
programmable trigger events, queue priorities, and so on.
When software-initiated continuous-scan mode is selected, 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 execution continues without pausing. When
the end-of-queue is reached, another internal trigger event is generated
and queue execution restarts at the beginning of the queue.
While the time to internally generate and act on a trigger event is very
short, the queue status field can be read as momentarily indicating that
the queue is idle. The trigger overrun flag is never set while in
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 result table can always be read to get the latest converted value for
each channel. The channels scanned are kept up to date by the QADC
without software involvement.
The software-initiated continuous-scan mode may be chosen for either
queue, but is normally used only with queue 2. When 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 slow-to-change analog channels. Interrupts are normally
not used with the software-initiated continuous-scan mode. Rather, the
Freescale Semiconductor, Inc.
For More Information On This Product,
Queued Analog-to-Digital Converter (QADC)
Go to: www.freescale.com
MMC2114 • MMC2113 • MMC2112 — Rev. 1.0
MOTOROLA