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Sheet目录3873

156页 157页 158页 159页 [160页]161页 162页 163页 164页

2010 Microchip Technology Inc.

DS41303G-page 31

PIC18F2XK20/4XK20

2.4.3

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 2-3). 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 2-3 and Figure 2-4 show typical circuits for

quartz crystal and ceramic resonators, respectively.

FIGURE 2-3:

QUARTZ CRYSTAL

OPERATION (LP, XT OR

HS MODE)

FIGURE 2-4:

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

to 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

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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