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Sheet目录3849

25页 26页 27页 28页 [29页]30页 31页 32页 33页

2010-2012 Microchip Technology Inc.

DS41412E-page 35

PIC18(L)F2X/4XK22

2.5.3

LP, XT, HS MODES

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

crystal resonators or ceramic resonators connected to

OSC1 and OSC2 (Figure 2-6). 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 offers a Medium Power (MP) and a

High Power (HP) option selectable by the FOSC<3:0>

bits. The MP selections are best suited for oscillator

frequencies between 4 MHz and 16 MHz. The HP

selection has the highest gain setting of the internal

inverter-amplifier and is best suited for frequencies

above 16 MHz. HS mode is best suited for resonators

that require a high drive setting.

FIGURE 2-6:

QUARTZ CRYSTAL

OPERATION (LP, XT OR

HS MODE)

FIGURE 2-7:

CERAMIC RESONATOR

OPERATION

(XT OR HS MODE)

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

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, refer to the

following Microchip Application 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

ceramic resonators with low drive level.

2: The value of RF varies with the Oscillator mode

selected (typically between 2 M

to 10 M.

3: An additional parallel feedback resistor (RP)

may be required for proper ceramic resonator

operation.

C2 Ceramic

RS(1)

OSC1/CLKIN

RF(2)

Sleep

To Internal

Logic

PIC MCU

RP(3)

Resonator

OSC2/CLKOUT

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