Motorola MPC533 Reference Manual page 467

Table 13-9. QASR0 Bit Descriptions (continued)
Bits Name
6:9 QS
10:15 CWP
External Trigger Single-scan
External Trigger Continuous-scan
Periodic/Interval Timer Trigger Single-scan
Periodic/Interval Timer Continuous-scan
Software Initiated Single-scan
Software Initiated Continuous-scan
MOTOROLA Chapter 13. Queued Analog-to-Digital Converter Legacy Mode Operation
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Queue Status
The 4-bit read-only QS field indicates the current condition of queue 1 and queue 2. The
following are the five queue status conditions:
Idle
Active
Paused
Suspended
Trigger pending
The two most significant bits are associated primarily with queue 1, and the remaining two
bits are associated with queue 2. Since the priority scheme between the two queues
causes the status to be interlinked, the status bits are considered as one 4-bit field.
Table 13-11 shows the bits in the QS field and how they affect the status of queue 1 and
queue 2. Refer to 13.6 "Trigger and Queue Interaction Examples," which shows the 4-bit
queue status field transitions in typical situations.
Command Word Pointer — The CWP allows the software to know which CCW is executing
at present, or was last completed. The command word pointer is a software read-only field,
and write operations have no effect. The CWP allows software to monitor the progress of
the QADC64E scan sequence. The CWP field is a CCW word pointer with a valid range of
0 to 63.
When a queue enters the paused state, the CWP points to the CCW with the pause bit set.
While in pause, the CWP value is maintained until a trigger event occurs on the same
queue or the other queue. Usually, the CWP is updated a few clock cycles before the queue
status field shows that the queue has become active. For example, software may read a
CWP pointing to a CCW in queue 2, and the status field shows queue 1 paused, queue 2
trigger pending.
When the QADC64E finishes the scan of the queue, the CWP points to the CCW where the
end-of-queue (EOQ) condition was detected. Therefore, when the end-of-queue condition
is a CCW with the EOQ code (channel 63), the CWP points to the CCW containing the
EOQ.
When the last CCW in a queue is in the last CCW table location (CCW63), and it does not
contain the EOQ code, the end-of-queue is detected when the following CCW is read, so
the CWP points to word CCW0.
Finally, when queue 1 operation is terminated after a CCW is read that is defined as BQ2,
the CWP points to the same CCW as BQ2.
During the stop mode, the CWP is reset to zero, since the control registers and the analog
logic are reset. When the freeze mode is entered, the CWP is unchanged; it points to the
last executed CCW.
Table 13-10. Pause Response
Scan Mode
Programming the QADC64E Registers
Description
Q Operation
Pauses
Pauses
Pauses
Pauses
Continues
Continues
PF Asserts?
Yes
Yes
Yes
Yes
Yes
Yes
13-23