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MPC561/MPC563 Reference Manual
MOTOROLA
Programming the QADC64E Registers
the CCWs in a queue or sub-queue. An “external trigger” is only one of the possible “trigger
events.”
A scan sequence may be initiated by the following:
A software command
Expiration of the periodic/interval timer
External trigger signal
External gated signal (queue 1 only)
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 - 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.
Final sample - 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 2, 4, 8, or 16 cycles.
Resolution - 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.