Motorola MPC533 Reference Manual page 461

Table 13-7. QACR2 Bit Descriptions (continued)
Bits Name
2 SSE2 Queue 2 Single-Scan Enable Bit — SSE2 enables a single-scan of queue 2 to start after a
trigger event occurs. The SSE2 bit may be set to a one during the same write cycle when the
MQ2 bits are set for one of the single-scan queue operating modes. The single-scan enable bit
can be written as a one or a zero, but is always read as a zero. The SSE2 bit enables a trigger
event to initiate queue execution for any single-scan operation on queue 2. The QADC64E
clears the SSE2 bit when the single-scan is complete. Refer to Table 13-8 for more information.
0 Trigger events are not accepted for single-scan modes
1 Accept a trigger event to start queue 2 in a single-scan mode
3:7 MQ2 Queue 2 Operating Mode — The MQ2 field selects the queue operating mode for queue 2.
Refer to Table 13-8 for more information.
8 RESUME 0 After suspension, begin executing with the first CCW in queue 2 or the current sub-queue
1 After suspension, begin executing with the aborted CCW in queue 2
9:15 BQ2 Beginning of queue 2 — The BQ2 field indicates the CCW location where queue 2 begins. To
allow the length of queue 1 and queue 2 to vary, a programmable pointer identifies the CCW
table location where queue 2 begins. The BQ2 field also serves as an end-of-queue condition
for queue 1. Setting BQ2 beyond physical CCW table memory space allows queue 1 all 64
entries.
Software defines the beginning of queue 2 by programming the BQ2 field in QACR2. BQ2 is
usually programmed before or at the same time as the queue operating mode for queue 2 is
selected. If BQ2 is 64 or greater, queue 2 has no entries, and the entire CCW table is dedicated
to queue 1 and CCW63 is the end-of-queue 1. If BQ2 is zero, the entire CCW table is dedicated
to queue 2. As a special case, when a queue operating mode for queue 1 is selected and a
trigger event occurs for queue 1 with BQ2 set to zero, queue 1 execution is terminated after
CCW0 is read. Conversions do not occur.
The BQ2 pointer may be changed dynamically, to alternate between queue 2 scan sequences.
A change in BQ2 after queue 2 has begun or if queue 2 has a trigger pending does not affect
queue 2 until queue 2 is started again.For example, two scan sequences could be defined as
follows: the first sequence starts at CCW10, with a pause after CCW11 and an EOQ
programmed in CCW15; the second sequence starts at CCW16, with a pause after CCW17 and
an EOQ programmed in CCW39.
With BQ2 set to CCW10 and the continuous-scan mode selected, queue execution begins.
When the pause is encountered in CCW11, a software interrupt routine can redefine BQ2 to be
CCW16. Therefore, after the end-of-queue is recognized in CCW15, an internal retrigger event
is generated and execution restarts at CCW16. When the pause software interrupt occurs
again, software can change BQ2 back to CCW10. After the end-of-queue is recognized in
CCW39, an internal retrigger event is created and execution now restarts at CCW10.
If BQ2 is changed while queue 1 is active, the effect of BQ2 as an end-of-queue indication for
queue 1 is immediate. However, beware of the risk of losing the end-of-queue 1 through moving
BQ2. Recommend use of EOQ (chan63) to end queue 1.
Table 13-8 shows the bits in the MQ2 field that enable different queue 2 operating modes.
MQ2[3:7]
00000
00001
00010
00011
MOTOROLA Chapter 13. Queued Analog-to-Digital Converter Legacy Mode Operation
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Table 13-8. Queue 2 Operating Modes
Disabled mode, conversions do not occur
Software triggered single-scan mode (started with SSE2)
External trigger rising edge single-scan mode
External trigger falling edge single-scan mode
Programming the QADC64E Registers
Description
Operating Modes
13-17