PIC18LF4331 datasheet(133/392 Pages) MICROCHIP

133 / 392 page

 2010 Microchip Technology Inc.

DS39616D-page 133

PIC18F2331/2431/4331/4431

13.2

Timer1 Oscillator

A crystal oscillator circuit is built in-between pins, T1OSI

(input) and T1OSO (amplifier output). It is enabled by

setting control bit, T1OSCEN (T1CON<3>). The oscilla-

tor is a low-power oscillator rated for 32 kHz crystals. It

will continue to run during all power-managed modes.

The circuit for a typical LP oscillator is shown in

Figure 13-3. Table 13-1 shows the capacitor selection

for the Timer1 oscillator.

The user must provide a software time delay to ensure

proper start-up of the Timer1 oscillator.

FIGURE 13-3:

EXTERNAL COMPONENTS

FOR THE TIMER1 LP

OSCILLATOR

TABLE 13-1:

CAPACITOR SELECTION FOR

THE TIMER OSCILLATOR

13.3

Timer1 Oscillator Layout

Considerations

The Timer1 oscillator for PIC18F2331/2431/4331/4431

devices incorporates an additional low-power feature.

When this option is selected, it allows the oscillator to

automatically reduce its power consumption when the

microcontroller is in Sleep mode. During normal device

operation, the oscillator draws full current. As high

noise environments may cause excessive oscillator

instability in Sleep mode, this option is best suited for

low noise applications, where power conservation is an

important design consideration.

The low-power option is enabled by clearing the

T1OSCMX bit (CONFIG3L<5>). By default, the option

is disabled, which results in a more or less constant

current draw for the Timer1 oscillator.

Due to the low-power nature of the oscillator, it may

also be sensitive to rapidly changing signals in close

proximity.

The oscillator circuit, shown in Figure 13-3, should be

located as close as possible to the microcontroller.

There should be no circuits passing within the oscillator

circuit boundaries other than VSS or VDD. Refer to

Section 2.0 “Guidelines for Getting Started with

PIC18F Microcontrollers”

for additional information

Osc Type

Freq

32 kHz

27 pF(1)

Note 1:

Microchip suggests this value as a starting

point in validating the oscillator circuit.

Higher capacitance increases the stabil-

ity of the oscillator, but also increases the

start-up time.

Since each resonator/crystal has its own

characteristics, the user should consult

the resonator/crystal manufacturer for

appropriate

values

external

components.

Capacitor values are for design guidance

only.

Note:

See the notes with Table 13-1 for additional

information about capacitor selection.

XTAL

PIC18FXXXX

T1OSI

T1OSO

32.768 kHz

27 pF

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