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Enhanced Queued Analog-to-Digital Converter (EQADC)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
1103
Figure 25-66. ETRIG Event Propagation Example
25.6.4.6
CFIFO Scan Trigger Modes
The EQADC supports two different scan modes, single-scan and continuous-scan. Refer to
for a summary of these two scan modes. When a CFIFO is triggered, the EQADC scan mode determines
whether the EQADC will stop command transfers from a CFIFO, and wait for software intervention to
rearm the CFIFO to detect new trigger events, upon detection of an asserted EOQ bit in the last transfer.
Refer to
Section 25.6.2.3, Message Format in EQADC
, for details about command formats.
CFIFOs can be configured in single-scan or continuous-scan mode. When a CFIFO is configured in
single-scan mode, the EQADC scans the CQueue one time. The EQADC stops future command transfers
from the triggered CFIFO after detecting the EOQ bit set in the last transfer. After a EOQ bit is detected,
software involvement is required to rearm the CFIFO so that it can detect new trigger events.
When a CFIFO is configured for continuous-scan mode, no software involvement is necessary to rearm
the CFIFO to detect new trigger events after an asserted EOQ is detected. In continuous-scan mode the
whole CQueue is scanned multiple times.
The EQADC also supports different triggering mechanisms for each scan mode. The EQADC will not
transfer commands from a CFIFO until the CFIFO is triggered. The combination of scan modes and
triggering mechanisms allows the support of different requirements for scanning input channels. The scan
mode and trigger mechanism are configured by programming the MODEx field in
EQADC CFIFO Control Registers (EQADC_CFCR)
Enabled CFIFOs can be triggered by software or external trigger events. The elapsed time from detecting
a trigger to transferring a command is a function of clock frequency, trigger synchronization, trigger
filtering or not, programmable trigger events, command transfer, CFIFO prioritization, CBuffer
availability, etc. Fast and predictable transfers can be achieved by ensuring that the CFIFO is not
underflowing and that the target CBuffer is not full when the CFIFO is triggered.
System Clock
External Trigger Signal
Filtered External
CFIFO Status
Trigger Signal
Signal State at Input Pin
MODEx
IDLE
WAITING FOR TRIGGER
TRIGGERED
DISABLED
CONTINUOUS SCAN HIGH LEVEL GATED EXTERNAL TRIGGER
Trigger Detection Delay
Trigger Synchronization and Filtering Delay (Obs. 1)
Obs.
- 1: This delay is about 2 clocks when the filter bypass control is asserted.
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