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27.8.2 Boundary Conditions
The queue operation boundary conditions are:
• The first CCW in a queue specifies channel 63, the end-of-queue (EOQ) code. The
queue becomes active and the first CCW is read. The end-of-queue is recognized,
the completion flag is set, and the queue becomes idle. A conversion is not
performed.
• BQ2 (beginning of queue 2) is set at the end of the CCW table (63) and a trigger
event occurs on queue 2. The end-of-queue condition is recognized, a conversion is
performed, the completion flag is set, and the queue becomes idle.
• BQ2 is set to CCW0 and a trigger event occurs on queue 1. After reading CCW0,
the end-of-queue condition is recognized, the completion flag is set, and the queue
becomes idle. A conversion is not performed.
• 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.
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.
MOTOROLA
Chapter 27. Queued Analog-to-Digital Converter (QADC)
NOTE
Digital Control Subsystem
27-49
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