SE33 datasheet(66/478 Pages) MICROCHIP

66 / 478 page

PIC16(L)F1946/47

DS41414D-page 66

 2010-2012 Microchip Technology Inc.

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<2:0> 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, OSC1/CLKIN is available for general

purpose I/O. OSC2/CLKOUT is available for general

purpose I/O or CLKOUT.

The function of the OSC2/CLKOUT pin is determined

by the CLKOUTEN bit in Configuration Words.

The internal oscillator block has two independent

oscillators and a dedicated Phase-Lock Loop, HFPLL

that can produce one of three internal system clock

sources.

The

HFINTOSC

(High-Frequency

Internal

Oscillator) is factory calibrated and operates at

16 MHz. The HFINTOSC source is generated

from the 500 kHz MFINTOSC source and the

dedicated Phase-Lock Loop, HFPLL. The

frequency

the

HFINTOSC

can

user-adjusted via software using the OSCTUNE

The MFINTOSC (Medium-Frequency Internal

Oscillator) is factory calibrated and operates at

500 kHz. The frequency of the MFINTOSC can

be user-adjusted via software using the

OSCTUNE register (Register 5-3).

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

frequency of the HFINTOSC can be altered via

software using the OSCTUNE register (Register 5-3).

The output of the HFINTOSC connects to a postscaler

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 5.2.2.7 “Internal

Oscillator Clock Switch Timing” for more information.

The HFINTOSC is enabled by:

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

•FOSC<2:0> = 100, 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 Status Locked

bit (HFIOFL) of the OSCSTAT register indicates when

the HFINTOSC is running within 2% of its final value.

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

MFINTOSC

The

Medium-Frequency

Internal

Oscillator

(MFINTOSC) is a factory calibrated 500 kHz internal

clock source. The frequency of the MFINTOSC can be

altered via software using the OSCTUNE register

(Register 5-3).

The output of the MFINTOSC connects to a postscaler

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

frequencies derived from the MFINTOSC can be

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

OSCCON register. See Section 5.2.2.7 “Internal

Oscillator Clock Switch Timing” for more information.

The MFINTOSC is enabled by:

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

•FOSC<2:0> = 100, or

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

OSCCON register to ‘1x’

The Medium-Frequency Internal Oscillator Ready bit

(MFIOFR) of the OSCSTAT register indicates when the

MFINTOSC is running.

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