Motorola ColdFire MCF5281 - Manual (Page 584)

Queued Analog-to-Digital Converter (QADC)
28-46 Freescale Semiconductor
• BQ2 (beginning of queue 2) is set beyond the end of the CCW table (64–127) and a trigger event
occurs on queue 2. The end-of-queue condition is recognized immediately, the completion flag is
set, and the queue becomes idle. A conversion is not performed.
NOTE
Multiple end-of-queue conditions may be recognized simultaneously,
although there is no change in QADC behavior. For example, if BQ2 is set
to CCW0, CCW0 contains the EOQ code, and a trigger event occurs on
queue 1, the QADC reads CCW0 and detects both end-of-queue conditions.
The completion flag is set and queue 1 becomes idle.
Boundary conditions also exist for combinations of pause and end-of-queue. One case is when a pause bit
is in one CCW and an end-of-queue condition is in the next CCW. The conversion specified by the CCW
with the pause bit set completes normally. The pause flag is set. However, because the end-of-queue
condition is recognized, the completion flag is also set and the queue status becomes idle, not paused.
Examples of this situation include:
• The pause bit is set in CCW5 and the channel 63 (EOQ) code is in CCW6.
• The pause is in CCW63.
• During queue 1 operation, the pause bit is set in CCW20 and BQ2 points to CCW21.
Another pause and end-of-queue boundary condition occurs when the pause and an end-of-queue
condition occur in the same CCW. Both the pause and end-of-queue conditions are recognized
simultaneously. The end-of-queue condition has precedence so a conversion is not performed for the CCW
and the pause flag is not set. The QADC sets the completion flag and the queue status becomes idle.
Examples of this situation are:
• The pause bit is set in CCW10 and EOQ is programmed into CCW10.
• During queue 1 operation, the pause bit set in CCW32, which is also BQ2.
28.8.3 Scan Modes
The QADC queuing mechanism allows application software to utilize different requirements for
automatically scanning input channels.
In single-scan mode, a single pass through a sequence of conversions defined by a queue is performed. In
continuous-scan mode, multiple passes through a sequence of conversions defined by a queue are
executed.
The possible modes are:
• Disabled mode and reserved mode
• Software-initiated single-scan mode
• Externally triggered single-scan mode
• Externally gated single-scan mode
• Interval timer single-scan mode
• Software-initiated continuous-scan mode
• Externally triggered continuous-scan mode
• Externally gated continuous-scan mode
• Periodic timer continuous-scan mode
The following paragraphs describe single-scan and continuous-scan operations.
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3