Microchip Technology DM164130-7 Data Sheet

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 

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.
1.

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 of the HFINTOSC can be
user-adjusted via software using the OSCTUNE
register (

2.

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 (

).

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 (

The output of the HFINTOSC connects to a postscaler
and multiplexer (see 

). One of multiple

frequencies derived from the HFINTOSC can be
selected via software using the IRCF<3:0> bits of the
OSCCON register. See 

 for more information.

The HFINTOSC is enabled by:
• Configure the IRCF<3:0> bits of the OSCCON 

register for the desired HF frequency, and

• 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
(

The output of the MFINTOSC connects to a postscaler
and multiplexer (see 

frequencies derived from the MFINTOSC can be
selected via software using the IRCF<3:0> bits of the
OSCCON register. See 

 for more information.

The MFINTOSC is enabled by:
• Configure the IRCF<3:0> bits of the OSCCON 

register for the desired HF frequency, and

• 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.