Datasheet

 2010-2012 Microchip Technology Inc. DS41414D-page 163
PIC16(L)F1946/47
16.1 ADC Configuration
When configuring and using the ADC the following
functions must be considered:
• Port configuration
• Channel selection
• ADC voltage reference selection
• ADC conversion clock source
• Interrupt control
• Result formatting
16.1.1 PORT CONFIGURATION
The ADC can be used to convert both analog and
digital signals. When converting analog signals, the I/O
pin should be configured for analog by setting the
associated TRIS and ANSEL bits. Refer to
Section 12.0 “I/O Ports” for more information.
16.1.2 CHANNEL SELECTION
There are 20 selections available:
• AN<16:0> pins
• Temperature Indicator
• DAC Output
• FVR (Fixed Voltage Reference) Output
Refer to
Section 15.0 “Temperature Indicator Mod-
ule”
, Section 17.0 “Digital-to-Analog Converter
(DAC) Module”
and Section 14.0 “Fixed Voltage
Reference (FVR)”
for more information on these chan-
nel selections.
The CHS bits of the ADCON0 register determine which
channel is connected to the sample and hold circuit.
When changing channels, a delay is required before
starting the next conversion. Refer to
Section 16.2
“ADC Operation”
for more information.
16.1.3 ADC VOLTAGE REFERENCE
The ADPREF bit of the ADCON1 register provides
control of the positive voltage reference. The positive
voltage reference can be:
•V
REF+ pin
•V
DD
The ADNREF bit of the ADCON1 register provides
control of the negative voltage reference. The negative
voltage reference can be:
•V
REF- pin
•V
SS
See Section 14.0 “Fixed Voltage Reference (FVR)”
for more details on the fixed voltage reference.
16.1.4 CONVERSION CLOCK
The source of the conversion clock is software select-
able via the ADCS bits of the ADCON1 register. There
are seven possible clock options:
•F
OSC/2
•F
OSC/4
•F
OSC/8
•F
OSC/16
•F
OSC/32
•F
OSC/64
•F
RC (dedicated internal oscillator)
The time to complete one bit conversion is defined as
T
AD. One full 10-bit conversion requires 11.5 TAD peri-
ods as shown in Figure 16-2.
For correct conversion, the appropriate T
AD specifica-
tion must be met. Refer to the A/D conversion require-
ments in
Section 30.0 “Electrical Specifications” for
more information. Table 16-1 gives examples of appro-
priate ADC clock selections.
Note: Analog voltages on any pin that is defined
as a digital input may cause the input buf-
fer to conduct excess current.
Note: Unless using the FRC, any changes in the
system clock frequency will change the
ADC clock frequency, which may
adversely affect the ADC result.