PIC18F2331/2431/4331/4431
21.1.3
CONVERSION SEQUENCING
21.1.5
A/D MODULE INITIALIZATION
STEPS
The ACMOD<1:0> bits control the sequencing of the
A/D conversions. When ACSCH = 0, the A/D is
configured to sample and convert a single channel.
The ACMOD bits select which group to perform the
conversions and the GxSEL<1:0> bits select which
channel in the group is to be converted. If Single-Shot
mode is enabled, the A/D interrupt flag will be set after
the channel is converted. If Continuous Loop mode is
enabled, the A/D interrupt flag will be set according to
the ADRS<1:0> bits.
The following steps should be followed to initialize the
A/D module:
1. Configure the A/D module:
a) Configure the analog pins, voltage reference
and digital I/O.
b) Select the A/D input channels.
c) Select the A/D Auto-Conversion mode
(Single-Shot or Continuous Loop).
d) Select the A/D conversion clock.
e) Select the A/D conversion trigger.
2. Configure the A/D interrupt (if required):
a) Set the GIE bit.
When ACSCH = 1, multiple channel sequencing is
enabled and two submodes can be selected. The first
mode is Sequential mode with two settings. The first set-
ting is called SEQM1, and first samples and converts the
selected Group A channel, and then samples and
converts the selected Group B channel. The second
mode is called SEQM2, and it samples and converts a
Group A channel, Group B channel, Group C channel
and finally, a Group D channel.
b) Set the PEIE bit.
c) Set the ADIE bit.
d) Clear the ADIF bit.
e) Select the A/D trigger setting.
f) Select the A/D interrupt priority.
3. Turn on ADC:
The second multiple channel sequencing submode is
Simultaneous Sampling mode. In this mode, there are
also two settings. The first setting is called STNM1, and
uses the two sample and hold circuits on the A/D
module. The selected Group A and B channels are
simultaneously sampled and then the Group A channel
is converted followed by the conversion of the Group B
channel. The second setting is called STNM2, and
starts the same as STNM1, but follows it with a
simultaneous sample of Group C and D channels. The
A/D module will then convert the Group C channel
followed by the Group D channel.
a) Set the ADON bit in the ADCON0 register.
b) Wait the required power-up setup time,
about 5-10 s.
4. Start the sample/conversion sequence:
a) Sample for a minimum of 2 TAD and start
the conversion by setting the GO/DONE bit.
The GO/DONE bit is set by the user in
software or by the module if initiated by a
trigger.
b) If TACQ is assigned a value (multiple of TAD),
then setting the GO/DONE bit starts a
sample period of the TACQ value, then starts
a conversion.
21.1.4
TRIGGERING A/D CONVERSIONS
The PIC18F2331/2431/4331/4431 devices are capable
of triggering conversions from many different sources.
The same method used by all other microcontrollers of
setting the GO/DONE bit still works. The other trigger
sources are:
5. Wait for A/D conversion/conversions to
complete using one of the following options:
a) Poll for the GO/DONE bit to be cleared if in
Single-Shot mode.
• RC3/INT0 Pin
b) Wait for the A/D Interrupt Flag (ADIF) to be
set.
• Timer5 Overflow
• Input Capture 1 (IC1)
• CCP2 Compare Match
• Power Control PWM Rising Edge
c) Poll for the BFEMT bit to be cleared to
signify that at least the first conversion has
completed.
These triggers are enabled using the SSRC<4:0> bits
(ADCON3<4:0>). Any combination of the five sources
can trigger a conversion by simply setting the corre-
sponding bit in ADCON3. When the trigger occurs, the
GO/DONE bit is automatically set by the hardware and
then cleared once the conversion completes.
6. Read the A/D results, clear the ADIF flag,
reconfigure the trigger.
DS39616D-page 248
2010 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
