16F1933 datasheet(57/464 Pages) MICROCHIP

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 2011-2012 Microchip Technology Inc.

DS41575C-page 57

PIC16(L)F1933

5.2.2

INTERNAL CLOCK SOURCES

The device may be configured to use the internal

oscillator 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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