PIC18F2420/2520/4420/4520
19.4 Operation in Power-Managed
Modes
19.5 Configuring Analog Port Pins
The ADCON1, TRISA, TRISB 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
CHS<3:0> bits and the TRIS bits.
a
power-managed mode, the ACQT<2:0> and
ADCS<2:0> bits in ADCON2 should be updated in
accordance with the clock source to be used in that
mode. After entering the mode, an A/D acquisition or
conversion may be started. Once started, the device
should continue to be clocked by the same clock
source until the conversion has been completed.
Note 1: When reading the PORT register, all pins
configured as analog input channels will
read as cleared (a low level). Pins con-
figured as digital inputs will convert as
analog inputs. Analog levels on a digitally
configured input will be accurately
converted.
If desired, the device may be placed into the
corresponding Idle mode during the conversion. If the
device clock frequency is less than 1 MHz, the A/D RC
clock source should be selected.
2: Analog levels on any pin defined as a dig-
ital input may cause the digital input buffer
to consume current out of the device’s
specification limits.
Operation in Sleep mode requires the A/D FRC clock to
be selected. If the ACQT<2:0> bits are set to ‘000’ 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 bit
(OSCCON<7>) must have already been cleared prior
to starting the conversion.
3: The PBADEN bit, in Configuration
Register 3H, configures PORTB pins to
reset as analog or digital pins by control-
ling how the PCFG bits in ADCON1 are
reset.
DS39631E-page 230
© 2008 Microchip Technology Inc.
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