PIC18F1220ESLASHSOSQTP datasheet(107/308 Pages) MICROCHIP

107 / 308 page

DS39605F-page 105

PIC18F1220/1320

12.2

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 oscil-

lator 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 12-3. Table 12-1 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 12-3:

EXTERNAL

COMPONENTS FOR THE

TIMER1 LP OSCILLATOR

TABLE 12-1:

CAPACITOR SELECTION FOR

THE TIMER OSCILLATOR

Note:

The Timer1 oscillator shares the T1OSI

and T1OSO pins with the PGD and PGC

pins

used

for

programming

and

debugging.

When using the Timer1 oscillator, In-Circuit

Serial

Programming

(ICSP)

may

not

function correctly (high voltage or low

voltage), or the In-Circuit Debugger (ICD)

may not communicate with the controller.

As a result of using either ICSP or ICD, the

Timer1 crystal may be damaged.

If ICSP or ICD operations are required, the

crystal should be disconnected from the

circuit (disconnect either lead), or installed

after programming. The oscillator loading

capacitors may remain in-circuit during

ICSP or ICD operation.

Osc Type

Freq

32 kHz

22 pF(1)

Note 1: Microchip suggests this value as a starting

point in validating the oscillator circuit.

Oscillator operation should then be tested

to ensure expected performance under

all

expected

conditions

(VDD

and

temperature).

2: Higher capacitance increases the stability

of the oscillator, but also increases the

start-up time.

3: Since each resonator/crystal has its own

characteristics, the user should consult

the resonator/crystal manufacturer for

appropriate

values

external

components.

4: Capacitor values are for design guidance

only.

Note:

See the Notes with Table 12-1 for additional

information about capacitor selection.

XTAL

PIC18FXXXX

PGD/T1OSI

PGC/T1OSO

32.768 kHz

22 pF

PGD

PGC

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