PIC16F877A-I/P【PDF 149/234 页】IC MCU FLASH 8KX14 EE 40DIP

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PIC18F2525/2620/4525/4620

DS39626E-page 230

2008 Microchip Technology Inc.

19.4

Operation in Power-Managed

Modes

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

a power-managed mode, the ACQT2:ACQT0 and

ADCS2:ADCS0 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.

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.

Operation in the Sleep mode requires the A/D FRC

clock to be selected. If bits ACQT2:ACQT0 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.

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 A/D operation is independent of the state of the

CHS3:CHS0 bits and the TRIS bits.

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 as

analog inputs. Analog levels on a digitally

configured

input

will

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.

3: The

PBADEN

bit

Configuration

reset as analog or digital pins by control-

ling how the PCFG<3:0> bits in ADCON1

are reset.

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