
PIC16(L)F1512/3
DS41624B-page 48
Preliminary
2012 Microchip Technology Inc.
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
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 that provides the internal system clock
source.
1.
The
HFINTOSC
(High-Frequency
Internal
Oscillator) is factory calibrated and operates at
16 MHz.
2.
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 output of the HFINTOSC connects to a postscaler
and multiplexer (see
Figure 5-1). The frequency derived
from the HFINTOSC can be selected via software using
the IRCF<3:0> bits of the OSCCON register. See
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 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 postscaler
and multiplexer (see
Figure 5-1). Select 31 kHz, via
software, using the IRCF<3:0> bits of the OSCCON
LFINTOSC is also the frequency for the Power-up Timer
(PWRT), Watchdog Timer (WDT) and Fail-Safe Clock
Monitor (FSCM).
The LFINTOSC is enabled by selecting 31 kHz
(IRCF<3:0> bits of the OSCCON register = 000) as the
system clock source (SCS bits of the OSCCON
register = 1x), or when any of the following are
enabled:
Configure the IRCF<3:0> bits of the OSCCON
register for the desired LF frequency, and
FOSC<2:0> = 100, 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)
Fail-Safe Clock Monitor (FSCM)
The Low-Frequency Internal Oscillator Ready bit
(LFIOFR) of the OSCSTAT register indicates when the
LFINTOSC is running.