PIC16F1503 datasheet(47/340 Pages) MICROCHIP

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 2011 Microchip Technology Inc.

Preliminary

DS41607A-page 47

PIC16(L)F1503

5.2.2

INTERNAL CLOCK SOURCES

The device may be configured to use the internal oscil-

lator block as the system clock by performing one of the

following actions:

• Program the FOSC<1:0> bits in Configuration

Words to select the INTOSC clock source, which

will be used as the default system clock upon a

device Reset.

• Write the SCS<1:0> bits in the OSCCON register

to switch the system clock source to the internal

oscillator during run-time. See Section 5.3

“Clock Switching”for more information.

In INTOSC mode, CLKIN is available for general

purpose I/O. CLKOUT is available for general purpose

I/O or CLKOUT.

The function of the CLKOUT pin is determined by the

CLKOUTEN bit in Configuration Words.

The internal oscillator block has two independent

oscillators clock sources.

The

HFINTOSC

(High-Frequency

Internal

Oscillator) is factory calibrated and operates at

16 MHz.

The

LFINTOSC

(Low-Frequency

Internal

Oscillator) is uncalibrated and operates at

31 kHz.

5.2.2.1

HFINTOSC

The High-Frequency Internal Oscillator (HFINTOSC) is

a factory calibrated 16 MHz internal clock source.

The outputs of the HFINTOSC connects to a prescaler

and multiplexer (see Figure 5-1). One of multiple

frequencies derived from the HFINTOSC can be

selected via software using the IRCF<3:0> bits of the

OSCCON register. See Section 5.2.2.4 “Internal

Oscillator Clock Switch Timing” for more information.

The HFINTOSC is enabled by:

• Configure the IRCF<3:0> bits of the OSCCON

•FOSC<1:0> = 00, or

• Set the System Clock Source (SCS) bits of the

OSCCON register to ‘1x’.

A fast start-up oscillator allows internal circuits to power

up and stabilize before switching to HFINTOSC.

The High-Frequency Internal Oscillator Ready bit

(HFIOFR) of the OSCSTAT register indicates when the

HFINTOSC is running.

The High-Frequency Internal Oscillator Stable bit

(HFIOFS) of the OSCSTAT register indicates when the

HFINTOSC is running within 0.5% of its final value.

5.2.2.2

LFINTOSC

The Low-Frequency Internal Oscillator (LFINTOSC) is

an uncalibrated 31 kHz internal clock source.

The output of the LFINTOSC connects to a multiplexer

(see Figure 5-1). Select 31 kHz, via software, using the

IRCF<3:0> bits of the OSCCON register. See

Section 5.2.2.4 “Internal Oscillator Clock Switch

Timing” for more information. The LFINTOSC is also

the frequency for the Power-up Timer (PWRT) and

Watchdog Timer (WDT).

The LFINTOSC is enabled by selecting 31 kHz

(IRCF<3:0> bits of the OSCCON register = 000x) as

the system clock source (SCS bits of the OSCCON

enabled:

• Configure the IRCF<3:0> bits of the OSCCON

•FOSC<1:0> = 00, or

• Set the System Clock Source (SCS) bits of the

OSCCON register to ‘1x’

Peripherals that use the LFINTOSC are:

• Power-up Timer (PWRT)

• Watchdog Timer (WDT)

The Low-Frequency Internal Oscillator Ready bit

(LFIOFR) of the OSCSTAT register indicates when the

LFINTOSC is running.

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