Datasheet

PIC16(L)F1782/3
DS41579D-page 150 Preliminary  2011-2012 Microchip Technology Inc.
17.1 ADC Configuration
When configuring and using the ADC the following
functions must be considered:
• Port configuration
• Channel selection
- Single-ended
- Differential
• ADC voltage reference selection
• ADC conversion clock source
• Interrupt control
• Result formatting
17.1.1 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 13.0 “I/O Ports” for more information.
17.1.2 CHANNEL SELECTION
There are up to 14 channel selections available:
• AN<13:8, 4:0> pins
• Temperature Indicator
• DAC_output
• FVR (Fixed Voltage Reference) Output
Refer to
Section 15.0 “Fixed Voltage Reference
(FVR)”
and Section 16.0 “Temperature Indicator
Module”
for more information on these channel
selections.
When converting differential signals, the negative input
for the channel is selected with the CHSN<3:0> bits of
the ADCON2 register. Any positive input can be paired
with any negative input to determine the differential
channel.
The CHS<4:0> bits of the ADCON0 register determine
which positive channel is selected.
When CHSN<3:0> = 1111 then the ADC is effectively
a single ended ADC converter.
When changing channels, a delay is required before
starting the next conversion.
17.1.3 ADC VOLTAGE REFERENCE
The ADPREF bits of the ADCON1 register provide
control of the positive voltage reference. The positive
voltage reference can be:
•V
REF+
•V
DD
• FVR Buffer1
The ADNREF bits of the ADCON1 register provide
control of the negative voltage reference. The negative
voltage reference can be:
•V
REF- pin
•V
SS
See Section 15.0 “Fixed Voltage Reference (FVR)”
for more details on the Fixed Voltage Reference.
17.1.4 CONVERSION CLOCK
The source of the conversion clock is software
selectable 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 FRC oscillator)
The time to complete one bit conversion is defined as
T
AD. One full 12-bit conversion requires 15 TAD periods
as shown in Figure 17-2.
For correct conversion, the appropriate T
AD specification
must be met. Refer to the ADC conversion requirements
in
Section 30.0 “Electrical Specifications” for more
information. Table 17-1 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.