QADC64E Legacy Mode Operation
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
13-19
shows the bits in the MQ2 field that enable different queue 2 operating modes.
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.
Note:
Be sure to do a mode change when changing BQ2 and setting SSE2. Setting BQ2 first
is recommended.
Table 13-13. Queue 2 Operating Modes
MQ2[3:7]
Operating Modes
00000
Disabled mode, conversions do not occur
00001
Software triggered single-scan mode (started with SSE2)
00010
External trigger rising edge single-scan mode
00011
External trigger falling edge single-scan mode
00100
Interval timer single-scan mode: time = QCLK period x 2
7
00101
Interval timer single-scan mode: time = QCLK period x 2
8
00110
Interval timer single-scan mode: time = QCLK period x 2
9
00111
Interval timer single-scan mode: time = QCLK period x 2
10
01000
Interval timer single-scan mode: time = QCLK period x 2
11
01001
Interval timer single-scan mode: time = QCLK period x 2
12
01010
Interval timer single-scan mode: time = QCLK period x 2
13
Table 13-12. QACR2 Bit Descriptions (continued)
Bits
Name
Description
Summary of Contents for MPC561
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