Datasheet

PIC16(L)F1516/7/8/9
DS41452C-page 52  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 C
LKOUTEN 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
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
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 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),
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.