Datasheet

 2010 Microchip Technology Inc. DS39616D-page 247
PIC18F2331/2431/4331/4431
21.1 Configuring the A/D Converter
The A/D Converter has two types of conversions, two
modes of operation and eight different Sequencing
modes. These features are controlled by the ACONV
bit (ADCON0<5>), ACSCH bit (ADCON0<4>) and
ACMOD<1:0> bits (ADCON0<3:2>). In addition, the
A/D channels are divided into four groups as defined
in the ADCHS register. Ta b le 2 1-1 shows the
sequence configurations as controlled by the ACSCH
and ACMOD<1:0> bits.
21.1.1 CONVERSION TYPE
Two types of conversions exist in the high-speed 10-bit
A/D Converter module that are selected using the
ACONV bit. Single-Shot mode allows a single conversion
or sequence to be enabled when ACONV = 0. At the end
of the sequence, the GO/DONE
bit will be automatically
cleared and the interrupt flag, ADIF, will be set. When
using Single-Shot mode and configured for
Simultaneous mode, STNM2, acquisition time must be
used to ensure proper conversion of the analog input
signals.
Continuous Loop mode allows the defined sequence to
be executed in a continuous loop when ACONV = 1. In
this mode, either the user can trigger the start of
conversion by setting the GO/DONE
bit, or one of the
A/D triggers can start the conversion. The interrupt flag,
ADIF, is set based on the configuration of the bits,
ADRS<1:0> (ADCON3<7:6>). In Simultaneous modes,
STNM1 and STNM2 acquisition time must be config-
ured to ensure proper conversion of the analog input
signals.
21.1.2 CONVERSION MODE
The ACSCH bit (ADCON0<4>) controls how many
channels are used in the configured sequence. When
clear, the A/D is configured for single channel conver-
sion and will convert the group selected by the
ACMOD<1:0> bits and the channel selected by the
GxSEL<1:0> bits (ADCHS register). When ACSCH = 1,
the A/D is configured for multiple channel conversion
and the sequence is defined by ACMOD<1:0>.
TABLE 21-1: AUTO-CONVERSION SEQUENCE CONFIGURATIONS
Mode ACSCH ACMOD<1:0> Description
Multi-Channel Sequential Mode 1
(SEQM1)
100Groups A and B are sampled and converted
sequentially.
Multi-Channel Sequential Mode 2
(SEQM2)
101Groups A, B, C and D are sampled and converted
sequentially.
Multi-Channel Simultaneous Mode 1
(STNM1)
110Groups A and B are sampled simultaneously and
converted sequentially.
Multi-Channel Simultaneous Mode 2
(STNM2)
111Groups A and B are sampled simultaneously, then
converted sequentially. Then, Group C and D are
sampled simultaneously, then converted
sequentially.
Single Channel Mode 1 (SCM1) 000Group A is sampled and converted.
Single Channel Mode 2 (SCM2) 001Group B is sampled and converted.
Single Channel Mode 3 (SCM3) 010Group C is sampled and converted.
Single Channel Mode 4 (SCM4) 011Group D is sampled and converted.