MC68336/376
QUEUED ANALOG-TO-DIGITAL CONVERTER MODULE
MOTOROLA
USER’S MANUAL
Rev. 15 Oct 2000
8-19
When the QADC encounters a CCW with the pause bit set, the queue enters the
paused state after completing the conversion specified in the CCW with the pause bit.
The pause flag is set and a pause software interrupt may optionally be issued. The sta-
tus of the queue is shown to be paused, indicating completion of a subqueue. The
QADC then waits for another trigger event to again begin execution of the next
subqueue.
8.12.2 Queue Boundary Conditions
A queue boundary condition occurs when one or more of the queue operating
parameters is configured in a way that will inhibit queue execution. One such boundary
condition is when the first CCW in a queue specified channel 63, the end-of-queue
(EOQ) code. In this case, the queue becomes active and the first CCW is read. The
EOQ code is recognized, the completion flag is set, and the queue becomes idle. A
conversion is not performed.
A similar situation occurs when BQ2 (beginning of queue 2 pointer) is set beyond the
end of the CCW table (between $28 and $3F) and a trigger event occurs for queue 2.
The EOQ condition is recognized immediately, the completion flag is set, and the
queue becomes idle. A conversion is not performed.
The QADC behaves the same way when BQ2 is set to CCW0 and a trigger event
occurs for queue 1. After reading CCW0, the EOQ condition is recognized, the com-
pletion flag is set, and the queue becomes idle. A conversion is not performed.
Multiple EOQ conditions may be recognized simultaneously, but the QADC will not
behave differently. One example is when BQ2 is set to CCW0, CCW0 contains the
EOQ code, and a trigger event occurs for queue 1. The QADC will read CCW0 and
recognize the queue 1 trigger event, detecting both as EOQ conditions. The comple-
tion flag will be set and queue 1 will become 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, since the end-of-queue condition is recognized, the com-
pletion 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 bit is set in CCW27.
During queue 1 operation, the pause bit is set in CCW14 and BQ2 points to
CCW15.
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 prece-
dence 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: