Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
18-68
Freescale Semiconductor
Figure 18-38. ETRIG Event Propagation Example
18.4.3.5
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 stops command transfers from a CFIFO, and waits 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 18.4.1.2, “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 command queue 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 command queue is scanned multiple times.
The eQADC also supports different triggering mechanisms for each scan mode. The eQADC does 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 MODE
n
field in
“eQADC CFIFO Control Registers 0–5 (EQADC_CFCRn)
.”
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, programmable trigger events, command transfer, CFIFO prioritization, ADC availability, etc.
Fast and predictable transfers can be achieved by ensuring that the CFIFO is not underflowing and that the
target ADC can accept commands when the CFIFO is triggered.
18.4.3.5.1
Disabled Mode
The MODE
n
field in
Section 18.3.2.6, “eQADC CFIFO Control Registers 0–5 (EQADC_CFCRn)
,” for
all of the CFIFOs can be changed from any other mode to disabled at any time. No trigger event can initiate
command transfers from a CFIFO which has its MODE field programmed to disabled.
External Trigger Signal
Signal State at Input Pin
Idle
Waiting for Trigger
Triggered
Disabled
Continuous-Scan High Level Gated External Trigger
System Clock
CFIFO Status
MODE
n
Filtered External
Trigger Signal
Trigger Synchronization & Filtering Delay
Trigger Detection Delay
Summary of Contents for MPC5565
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