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PIC16(L)F1512/3
DS41624B-page 146
Preliminary
2012 Microchip Technology Inc.
16.6
Automated Capacitive Voltage
Divider
16.6.1
CONVERSION SEQUENCE
The conversion sequence can be expanded into three
stages; pre-charge time, acquisition time, and conversion.
these stages.
16.6.2
PRE-CHARGE TIMER
The pre-charge stage is an optional 1-127 instruction
cycle time used to put the external ADC channel and
the internal sample and hold capacitor (CHOLD) into
preconditioned states. The pre-charge stage of
conversion is enabled by writing a non-zero value to
the ADPRE<6:0> bits of the AADPRE register. This
stage is initiated when a conversion sequence is
started by either the GO/DONE bit or a Special Event
Trigger. When initiating an ADC conversion, if the
ADPRE bits are cleared, this stage is skipped.
During the pre-charge time, CHOLD is shorted to either
VDD or VSS, depending on the value of the ADIPPOL bit
of the AADCON3 register. The port pin logic of the
selected analog channel is overridden to drive a digital
high or low out. The output polarity of this override is
determined by the ADEPPOL bit of the AADCON3
register.
When the ADOOEN bit of the AADCON3 register is set,
then the ADOUT pin is overridden during pre-charge.
This override functions the same as the channel pin
overrides, but the polarity is selected by the ADIPPOL bit.
Even though the analog channel of the pin is selected,
the analog multiplexer is forced open during the pre-
charge stage. The ADC multiplexor logic is overridden
and disabled only during the pre-charge time.
16.6.3
ACQUISITION TIMER
The acquisition time is used to either acquire the signal
or to charge share. The acquisition time counts from 1
to 127 instruction cycle times and is used to allow the
voltage on the internal sample and hold capacitor
(CHOLD) to charge or discharge from the selected
analog channel. The acquisition time of conversion is
enabled by writing a non-zero value to the
ADACQ<6:0> bits of the AADACQ register. When the
acquisition time is enabled, the time starts immediately
follow the pre-charge stage. Otherwise, the acquisition
time is initiated by either setting the GO/DONE bit or a
Special Event Trigger.
At the start of the acquisition stage, the selected ADC
channel is connected to CHOLD. This allows charge
sharing between the pre-charged channel and the
16.6.4
STARTING A CONVERSION
To enable the ADC module, the ADON bit of the
AADCON0 register must be set to a ‘1’. Setting the GO/
DONE bit of the AADCON0 register to a ‘1’ in software
or by the Special Event Trigger inputs, will start the
Analog-to-Digital conversion.
Once a conversion begins, it proceeds until complete,
while ADON is set. If ADON is cleared (disabled by
software), the conversion is halted. The GO/DONE
status bit of the AADCON0 register indicates that a
conversion is occurring, regardless of the starting trigger.
16.6.5
COMPLETION OF A CONVERSION
When the conversion is complete, the ADC module will:
Clear the GO/DONE bit
Set the ADIF Interrupt Flag bit
Update the AADRESxH and AADRESxL registers
with new conversion result
16.6.6
TERMINATING A CONVERSION
If a conversion must be terminated before completion,
the GO/DONE bit can be cleared in software. The
AADRESxH and AADRESxL registers will be updated
with the partially complete Analog-to-Digital conversion
sample. Incomplete bits will match the last bit
converted.
16.6.7
DOUBLE SAMPLE CONVERSION
Double sampling can be enabled by the ADDSEN bit of
the AADCON3 register. When this bit is set, two
conversions are completed by each initiation of the GO/
DONE bit or a Special Event Trigger. The GO/DONE bit
stays set for the duration of both conversions and can
be used to cancel a conversion early.
The first conversion is written to the AADRES0H and
AADRES0L registers.
The second conversion starts two clock cycles after the
first has completed and the GO/DONE bit remains set.
When the ADIPEN bit of AADCON3 is set, the value
used by the ADC for the ADEPPOL, ADIPPOL, and
GRDPOL bits is inverted. The value stored in those bit
locations is unchanged. All other control signals remain
unchanged from the first conversion. The result of the
second conversion is stored in the AADRES1H and
Note:
The GO/DONE bit should not be set in the
same instruction that turns on the ADC.
Note:
A device Reset forces all registers to their
Reset state. Thus, the ADC module is
turned off and any pending conversion is
terminated.