MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 19-67
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 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 MODEn field in Section 19.3.2.6,
“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.
19.4.3.5.1 Disabled Mode
The MODEn field in Section 19.3.2.6, “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.
NOTE
If MODEn is not disabled, it must not be changed to any other mode besides
disabled. If MODEn is disabled and the CFIFO status is IDLE, MODEn can
be changed to any other mode.
If MODEn is changed to disabled:
• The CFIFO execution status will change to IDLE. The timing of this change depends on whether
a command is being transferred or not:
— When no command transfer is in progress, the eQADC switches the CFIFO to IDLE status
immediately.
— When a command transfer to an on-chip ADC is in progress, the eQADC will complete the
transfer, update TC_CF, and switch CFIFO status to IDLE. Command transfers to the internal
ADCs are considered completed when a command is written to the relevant buffer.
— When a command transfer to an external command buffer is in progress, the eQADC will abort
the transfer and switch CFIFO status to IDLE. If the eQADC cannot abort the transfer, that is
when the 26th bit of the serial message has being already shifted out, the eQADC will complete
the transfer, update TC_CF and then switch CFIFO status to IDLE.
• The CFIFOs are not invalidated automatically. The CFIFO still can be invalidated by writing a 1
to the CFINVn bit (see Section 19.3.2.6). Certify that CFS has changed to IDLE before setting
CFINVn.
• The TC_CFn
value also is not reset automatically, but it can be reset by writing 0 to it.
• The EQADC_FISRn[SSS] bit (see Section 19.3.2.8) is negated. The SSS bit can be set even if a 1
is written to the EQADC_CFCR[SSE] bit (see Section 19.3.2.6) in the same write that the MODEn
field is changed to a value other than disabled.
• The trigger detection hardware is reset. If MODEn is changed from disabled to an edge trigger
mode, a new edge, matching that edge trigger mode, is needed to trigger the command transfers
from the CFIFO.
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