Datasheet

Table Of Contents
PIC16(L)F1508/9
DS40001609C-page 136 2011-2013 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 TRIS and ANSEL bits. Refer to
Section 11.0 “I/O Ports for more information.
15.1.2 CHANNEL SELECTION
There are 15 channel selections available:
•AN<11:0> 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
ADPREF 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 select-
able via the ADCS bits of the ADCON1 register. There
are seven possible clock options:
•F
OSC/2
•FOSC/4
•FOSC/8
•F
OSC/16
•FOSC/32
•FOSC/64
FRC (internal RC 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 15-2.
For correct conversion, the appropriate T
AD specifica-
tion must be met. Refer to the ADC conversion require-
ments in Section 29.0 “Electrical Specifications” for
more information. Table 15-1 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
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.