PIC18F2331/2431/4331/4431
21.7 Operation in Power-Managed
Modes
21.8 Configuring Analog Port Pins
The ANSEL0, ANSEL1, TRISA and TRISE registers all
configure the A/D port pins. The port pins needed as
analog inputs must have their corresponding TRIS bits
set (input). If the TRIS bit is cleared (output), the digital
output level (VOH or VOL) will be converted.
The selection of the automatic acquisition time and A/D
conversion clock is determined in part by the clock
source and frequency while in a power-managed mode.
If the A/D is expected to operate while the device is in
The A/D operation is independent of the state of the
ANSEL0, ANSEL1 and TRIS bits.
a
power-managed mode, the ACQT<3:0> and
ADCS<2:0> bits in ADCON2 should be updated in
accordance with the power-managed mode clock that
will be used. After the power-managed mode is entered
(either of the power-managed Run modes), an A/D
acquisition or conversion may be started. Once an
acquisition or conversion is started, the device should
continue to be clocked by the same power-managed
mode clock source until the conversion has been com-
pleted. If desired, the device may be placed into the
corresponding power-managed Idle mode during the
conversion.
Note 1: When reading the PORT register, all pins
configured as analog input channels will
read as cleared (a low level). Pins
configured as digital inputs will convert an
analog input. Analog levels on a digitally
configured input will be accurately
converted.
2: Analog levels on any pin defined as a
digital input may cause the digital input
buffer to consume current out of the
device’s specification limits.
If the power-managed mode clock frequency is less
than 1 MHz, the A/D RC clock source should be
selected.
Operation in Sleep mode requires the A/D RC clock to
be selected. If bits, ACQT<3:0>, are set to ‘0000’ and
a conversion is started, the conversion will be delayed
one instruction cycle to allow execution of the SLEEP
instruction and entry to Sleep mode. The IDLEN and
SCS bits in the OSCCON register must have already
been cleared prior to starting the conversion.
Note:
The A/D can operate in Sleep mode only
when configured for Single-Shot mode. If
the part is in Sleep mode, and it is possible
for a source other than the A/D module to
wake the part, the user must poll
ADCON0<GO/DONE> to ensure it is clear
before reading the result.
DS39616D-page 252
2010 Microchip Technology Inc.
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