Motorola ColdFire MCF5281 - Manual (Page 552)

Queued Analog-to-Digital Converter (QADC)
28-14 Freescale Semiconductor
28.6.5.3 QADC Control Register 2 (QACR2)
QACR2 is the mode control register for queue 2. This register governs queue operating mode and the use
of completion and/or pause interrupts. Typically, these bits are written once when the QADC is initialized
and not changed thereafter.
QACR2 also includes a resume feature that selects the resumption point for queue 2 after its operation is
suspended by a queue 1 trigger event. The primary reason for selecting re-execution of the entire queue or
subqueue is to guarantee that all samples are taken consecutively in one scan (coherency).
When subqueues are not used, queue 2 execution restarts after suspension with the first CCW in queue 2.
When a pause has previously occurred in queue 2 execution, queue execution restarts after suspension with
the first CCW in the current subqueue.
A subqueue is considered to be a stand-alone sequence of conversions. Once a pause flag has been set to
report subqueue completion, that subqueue is not repeated until all CCWs in queue 2 are executed.
For example, the RESUME bit can be used when the frequency of queue 1 trigger events prohibit queue
2 completion. If the rate of queue 1 execution is too high, it is best for queue 2 execution to continue with
the CCW that was being converted when queue 2 was suspended. This allows queue 2 to eventually
complete execution.
The beginning of queue 2 is defined by programming the BQ2 field in QACR2. BQ2 is usually set before
or at the same time as the queue operating mode for queue 2 is selected. If BQ2[6:0]
≥ 64, queue 2 has no
entries, the entire CCW table is dedicated to queue 1, and CCW63 is the end-of-queue 1. If BQ2[6:0] is 0,
the entire CCW table is dedicated to queue 2. A special case occurs when an operating mode is selected
10000 Reserved mode
10001 Software-triggered continuous-scan mode
10010 External-trigger rising-edge continuous-scan mode
10011 External-trigger falling-edge continuous-scan mode
10100 Periodic timer continuous-scan mode: time = QCLK period
×
2 7
10101 Periodic timer continuous-scan mode: time = QCLK period
×
2 8
10110 Periodic timer continuous-scan mode: time = QCLK period
×
2
9
10111 Periodic timer continuous-scan mode: time = QCLK period
×
2
10
11000 Periodic timer continuous-scan mode: time = QCLK period
×
2
11
11001 Periodic timer continuous-scan mode: time = QCLK period
×
2
12
11010 Periodic timer continuous-scan mode: time = QCLK period
×
2
13
11011 Periodic timer continuous-scan mode: time = QCLK period
×
2
14
11100 Periodic timer continuous-scan mode: time = QCLK period
×
2
15
11101 Periodic timer continuous-scan mode: time = QCLK period
×
2
16
11110 Periodic timer continuous-scan mode: time = QCLK period
×
2
17
11111 Externally gated continuous-scan mode
Table 28-7. Queue 1 Operating Modes (continued)
MQ1[12:8] Operating Mode
MCF5282 and MCF5216 ColdFire Microcontroller User’s Manual, Rev. 3