Datasheet
PIC12(L)F1571/2
DS40001723D-page 130 2013-2015 Microchip Technology Inc.
15.1 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
15.1.1 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 TRISx and ANSELx bits. Refer to
Section 11.0 “I/O Ports” for more information.
15.1.2 CHANNEL SELECTION
There are 7 channel selections available:
• AN<3:0> pins
• Temperature Indicator
• DAC1_output
• FVR_buffer1
The CHS bits of the ADCON0 register determine which
channel is connected to the sample and hold circuit.
When changing channels, a delay (T
ACQ) is required
before starting the next conversion. Refer to
Section 15.2.6 “ADC Conversion Procedure” for
more information.
15.1.3 ADC VOLTAGE REFERENCE
The ADC module uses a positive and a negative
voltage reference. The positive reference is labeled
ref+ and the negative reference is labeled ref-.
The positive voltage reference (ref+) is selected by the
ADPREFx bits in the ADCON1 register. The positive
voltage reference source can be:
•V
REF+ pin
•V
DD
The negative voltage reference (ref-) source is:
•V
SS
15.1.4 CONVERSION CLOCK
The source of the conversion clock is software-selectable
via the ADCSx bits of the ADCON1 register. There are
seven possible clock options:
•F
OSC/2
•F
OSC/4
•FOSC/8
•FOSC/16
•F
OSC/32
•FOSC/64
• FRC (internal Fast RC oscillator)
The time to complete one bit conversion is defined as
T
AD. One full 10-bit conversion requires 11.5 TAD
periods, as shown in Figure 15-2.
For correct conversion, the appropriate T
AD specification
must be met. Refer to the ADC conversion requirements
in Section 26.0 “Electrical Specifications” for more
information. Table 15-1 gives examples of appropriate
ADC clock selections.
Note: Analog voltages on any pin that is defined
as a digital input may cause the input
buffer 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.