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2010 Microchip Technology Inc.

Preliminary

DS41350E-page 19

PIC18F/LF1XK50

2.5

Internal Oscillator

The internal oscillator module contains two independent

oscillators which are:

LFINTOSC: Low-Frequency Internal Oscillator

HFINTOSC: High-Frequency Internal Oscillator

When operating with either oscillator, OSC1 will be an

I/O and OSC2 will be either an I/O or CLKOUT. The

CLKOUT function is selected by the FOSC bits of the

CONFIG1H Configuration register. When OSC2 is

configured as CLKOUT, the frequency at the pin is the

frequency of the Internal Oscillator divided by 4.

2.5.1

LFINTOSC

The Low-Frequency Internal Oscillator (LFINTOSC) is

a 31 kHz internal clock source. The LFINTOSC

oscillator is the clock source for:

Power-up Timer

Watchdog Timer

Fail-Safe Clock Monitor

The LFINTOSC is enabled when any of the following

conditions are true:

Power-up Timer is enabled (PWRTEN = 0)

Watchdog Timer is enabled (WDTEN = 1)

Watchdog Timer is enabled by software

(WDTEN = 0 and SWDTEN = 1)

Fail-Safe Clock Monitor is enabled (FCMEM = 1)

SCS1 = 1 and IRCF<2:0> = 000 and INTSRC = 0

FOSC<3:0> selects the internal oscillator as the

primary clock and IRCF<2:0> = 000 and

INTSRC = 0

IESO = 1 (Two-Speed Start-up) and

IRCF<2:0> = 000 and INTSRC = 0

2.5.2

HFINTOSC

The High-Frequency Internal Oscillator (HFINTOSC) is

a precision oscillator that is factory-calibrated to

operate at 16 MHz. The output of the HFINTOSC

connects to a postscaler and a multiplexer (see

Figure 2-1). One of eight frequencies can be selected

using the IRCF<2:0> bits of the OSCCON register. The

following

frequencies

are

available

from

the

HFINTOSC:

16 MHZ

8 MHZ

4 MHZ

2 MHZ

1 MHZ (Default after Reset)

500 kHz

250 kHz

31 kHz

The HFIOFS bit of the OSCCON register indicates

whether the HFINTOSC is stable.

The HFINTOSC is enabled if any of the following

conditions are true:

SCS1 = 1 and IRCF<2:0>

000

SCS1 = 1 and IRCF<2:0> = 000 and INTSRC = 1

FOSC<3:0> selects the internal oscillator as the

primary clock and

- IRCF<2:0>

000 or

- IRCF<2:0> = 000 and INTSRC = 1

IESO = 1 (Two-Speed Start-up) and

- IRCF<2:0>

000 or

- IRCF<2:0> = 000 and INTSRC = 1

FCMEM = 1 (Fail Safe Clock Monitoring) and

- IRCF<2:0>

000 or

- IRCF<2:0> = 000 and INTSRC = 1

Note 1: Selecting 31 kHz from the HFINTOSC

oscillator requires IRCF<2:0> = 000 and

the INTSRC bit of the OSCTUNE register

to be set. If the INTSRC bit is clear, the

system

clock

will

come

from

the

LFINTOSC.

2: Additional adjustments to the frequency

of the HFINTOSC can made via the

OSCTUNE registers. See Register 2-3

for more details

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