MPC555CME Freescale Semiconductor, MPC555CME Datasheet - Page 435

• Manufacturer Part Number: MPC555CME
• Description: KIT EVALUATION FOR MPC555
• Manufacturer: Freescale Semiconductor
• Type: Microcontrollerr

Specifications of MPC555CME

• Contents: Module Board, Installation Guide, Power Supply, Cable, Software and more
• Processor To Be Evaluated: MPC555
• Data Bus Width: 32 bit
• Interface Type: RS-232
• For Use With/related Products: MPC555
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

MPC555
USER’S MANUAL
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 QADC64 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 con-
verting 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. Data read at different locations, however, may or may not be
coherent (that is, from the same queue scan sequence).
External Trigger Continuous-Scan Mode. The QADC64 provides external trigger
pins for both queues. When the external trigger software initiated continuous-scan
mode is selected, a transition on the associated external trigger pin initiates queue ex-
ecution. The polarity of the external trigger signal is programmable, so that the soft-
ware can choose to begin queue execution on the rising or falling edge. Each CCW is
read and the indicated conversions are performed until an end-of-queue condition is
encountered. When the next external trigger edge is detected, the queue execution
begins again automatically. Software initialization is not needed between trigger
events.
When a pause bit is encountered in external trigger continuous-scan mode, another
trigger event is required for queue execution to continue. Software involvement is not
needed to enable queue execution to continue from the paused state.
Some applications need to synchronize the sampling of analog channels to external
events. There are cases when it is not possible to use software initiation of the queue
scan sequence, since interrupt response times vary.
External Gated Continuous-Scan Mode. The QADC64 provides external gating for
queue 1 only. When external gated continuous-scan mode is selected, a transition on
the associated external trigger pin initiates queue execution. The polarity of the exter-
nal gated signal is fixed so a high level opens the gate and a low level closes the gate.
Once the gate is open, each CCW is read and the indicated conversions are per-
formed until the gate is closed. When the gate opens again, the queue execution au-
tomatically begins again from the beginning of the queue. Software initialization is not
needed between trigger events. If a pause in a CCW is encountered, the pause flag
will not set, and execution continues without pausing.
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MPC556 QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE-64
Rev. 15 October 2000
MOTOROLA
13-23