Motorola ColdFire MCF5281 User Manual
Page 553
Queued Analog-to-Digital Converter (QADC)
Freescale Semiconductor
28-15
for queue 1 and a trigger event occurs for queue 1 with BQ2 set to 0. Queue 1 execution starts momentarily,
but is terminated after CCW0 is read. No conversions occur.
The BQ2[6:0] pointer may be changed dynamically to alternate between queue 2 scan sequences. A
change in BQ2 after queue 2 has begun or when queue 2 has a trigger pending does not affect queue 2 until
it 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 end of queue (EOQ) programmed in CCW15; the second
sequence starts at CCW16, with a pause after CCW17 and an EOQ programmed in CCW39.
With BQ2[6:0] set to CCW10 and the continuous-scan mode selected, queue execution begins. When the
pause is encountered in CCW11, an interrupt service routine can retarget BQ2[6:0] to CCW16. When 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, BQ2 can be changed 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[6:0] is changed while queue 1 is active, the effect of BQ2[6:0] as an end-of-queue indication for
queue 1 is immediate. However, beware of the risk of losing the end-of-queue 1 when changing BQ2[6:0].
Using EOQ (channel 63) to end queue 1 is recommended.
NOTE
If BQ2[6:0] was assigned to the CCW that queue 1 is currently working on,
then that conversion is completed before the change to BQ2[6:0] takes
effect.
Each time a CCW is read for queue 1, the CCW location is compared with the current value of the
BQ2[6:0] pointer to detect a possible end-of-queue condition. For example, if BQ2[6:0] is changed to
CCW3 while queue 1 is converting CCW2, queue 1 is terminated after the conversion is completed.
However, if BQ2[6:0] is changed to CCW1 while queue 1 is converting CCW2, the QADC would not
recognize a BQ2[6:0] end-of-queue condition until queue 1 execution reached CCW1 again, presumably
on the next pass through the queue.
Stop mode resets this register (0x007f)
15
14
13
12
11
10
9
8
Field
CIE2
PIE2
SSE2
MQ212
MQ211
MQ210
MQ29
MQ28
Reset
0000_0000
R/W:
R/W
7
6
5
4
3
2
1
0
Field RESUME
BQ26
BQ25
BQ24
BQ23
BQ22
BQ21
BQ20
Reset
0111_1111
R/W:
R/W
Address
IPSBAR + 0x19_000e, 0x19_000f
Figure 28-10. QADC Control Register 2 (QACR2)
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3