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Sheet目录3873

74页 75页 76页 77页 [78页]79页 80页 81页 82页

2010 Microchip Technology Inc.

Preliminary

DS41350E-page 17

PIC18F/LF1XK50

2.3.1

PRIMARY EXTERNAL OSCILLATOR

SHUT-DOWN

The Primary External Oscillator can be enabled or dis-

abled via software. To enable software control of the

Primary External Oscillator, the PCLKEN bit of the

CONFIG1H Configuration register must be set. With

the PCLKEN bit set, the Primary External Oscillator is

controlled by the PRI_SD bit of the OSCCON2 register.

The Primary External Oscillator will be enabled when

the PRI_SD bit is set, and disabled when the PRI_SD

bit is clear.

2.3.2

LP, XT AND HS OSCILLATOR

MODES

The LP, XT and HS modes support the use of quartz

crystal resonators or ceramic resonators connected to

OSC1 and OSC2 (Figure 2-2). The mode selects a low,

medium or high gain setting of the internal inverter-

amplifier to support various resonator types and speed.

LP Oscillator mode selects the lowest gain setting of the

internal inverter-amplifier. LP mode current consumption

is the least of the three modes. This mode is best suited

to drive resonators with a low drive level specification, for

example, tuning fork type crystals.

XT Oscillator mode selects the intermediate gain

setting of the internal inverter-amplifier. XT mode

current consumption is the medium of the three modes.

This mode is best suited to drive resonators with a

medium drive level specification.

HS Oscillator mode selects the highest gain setting of the

internal inverter-amplifier. HS mode current consumption

is the highest of the three modes. This mode is best

suited for resonators that require a high drive setting.

Figure 2-2 and Figure 2-3 show typical circuits for

quartz crystal and ceramic resonators, respectively.

FIGURE 2-2:

QUARTZ CRYSTAL

OPERATION (LP, XT OR

HS MODE)

Note:

The Primary External Oscillator cannot be

shut down when it is selected as the

System Clock. To shut down the oscillator,

the system clock source must be either

the Secondary Oscillator or the Internal

Oscillator.

Note 1: Quartz

crystal

characteristics

vary

according

type,

package

and

manufacturer. The user should consult the

manufacturer data sheets for specifications

and recommended application.

2: Always verify oscillator performance over

the VDD and temperature range that is

expected for the application.

3: For oscillator design assistance, reference

the following Microchip Applications Notes:

AN826, “Crystal Oscillator Basics and

Crystal Selection for rfPIC and PIC

Devices” (DS00826)

AN849, “Basic PIC Oscillator Design”

(DS00849)

AN943, “Practical PIC Oscillator

Analysis and Design” (DS00943)

AN949, “Making Your Oscillator Work”

(DS00949)

Note 1:

A series resistor (RS) may be required for

quartz crystals with low drive level.

The value of RF varies with the Oscillator mode

selected (typically between 2 M

to 10 M.

Quartz

RS(1)

OSC1/CLKIN

RF(2)

Sleep

To Internal

Logic

PIC MCU

Crystal

OSC2/CLKOUT

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