Enhanced Queued Analog-to-Digital Converter (eQADC)
MPC5565 Microcontroller Reference Manual, Rev. 1.0
Freescale Semiconductor
18-87
In general, received data is moved into RFIFOs as they become available, while an exception happens
when multiple results from different sources become available at the same time. In that case, result data
from ADC0 is processed first, result data from ADC1 is only processed after all ADC0 data is processed,
and result data from the external device is only processed after all data from ADC0/1 is processed.
When time-stamped results return from the on-chip ADCs, the conversion result and the time stamp are
always moved to the RFIFOs in consecutive clock cycles to guarantee they are always stored in
consecutive RFIFO entries.
18.4.5
On-Chip ADC Configuration and Control
18.4.5.1
Enabling and Disabling the on-chip ADCs
The on-chip ADCs have an enable bit (ADC0_CR[ADC0_EN] and ADC1_CR[ADC1_EN], see
Section 18.3.3.1, “ADCn Control Registers (ADC0_CR and ADC1_CR)
”) which allows the enabling of
the ADCs only when necessary. When the enable bit for an ADC is negated, the clock input to that ADC
is stopped. The ADCs are disabled out of reset - ADC0/1_EN bits are negated - to allow for their safe
configuration. The ADC must only be configured when its enable bit is negated. After the enable bit of an
ADC is asserted, clock input is started, and the bias generator circuit is turned on. When the enable bits of
both ADCs are negated, the bias circuit generator is stopped.
NOTE
Conversion commands sent to a disabled ADC are ignored by the ADC
control hardware.
NOTE
An 8ms wait time from VDDA power up to enabling ADC is required to
pre-charge the external 100nf capacitor on REFBYPC. This time must be
guaranteed by the crystal startup time plus the reset duration, or the host
application. The ADC internal bias generator circuit starts up after 10
υ
s
upon VRH/VRL power up and produces a stable/required bias current to the
pre-charge circuit, but the current to the other analog circuits are disabled
until ADCs are enabled. As soon as the ADCs are enabled, the bias currents
to other analog circuits are ready.
NOTE
Because of previous design versions, the EQADC always waits 120 ADC
clocks before issuing the first conversion command following the enabling
of one of on-chip ADCs, or the exiting of stop mode. There are two
independent counters checking for this delay: one clocked by ADC0_CLK
and another by ADC1_CLK. Conversion commands can start to be executed
whenever one of these counters completes counting 120 ADC clocks.
[NOTE TO MIKE GARRARD: the implication of this paragraph is that teh
two clocks are the ADC timebases. is this the case? (Mike Garrard, can you
check this one out) can they be read, or even polled to see if 120 ADC clocks
is finished?]
Содержание MPC5565
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