Datasheet

PIC10(L)F320/322
DS41585A-page 28 Preliminary  2011 Microchip Technology Inc.
4.2 Clock Source Modes
Clock source modes can be classified as external or
internal.
• Internal clock source (INTOSC) is contained
within the oscillator module, which has eight
selectable output frequencies, with a maximum
internal frequency of 16 MHz.
• The External Clock mode (EC) relies on an
external signal for the clock source.
The system clock can be selected between external or
internal clock sources via the FOSC bit of the
Configuration Word.
4.3 Internal Clock Modes
The internal clock sources are contained within the
oscillator module. The internal oscillator block has two
internal oscillators that are used to generate all internal
system clock sources: the 16 MHz High-Frequency
Internal Oscillator (HFINTOSC) and the 31 kHz
(LFINTOSC).
The HFINTOSC consists of a primary and secondary
clock. The secondary clock starts first with rapid start-
up time, but low accuracy. The secondary clock ready
signal is indicated with the HFIOFR bit of the OSCCON
register. The primary clock follows with slower start-up
time and higher accuracy. The primary clock is stable
when the HFIOFS bit of the OSCCON register bit goes
high.
4.3.1 INTOSC MODE
When the FOSC bit of the Configuration Word is
cleared, the INTOSC mode is selected. When INTOSC
is selected, CLKIN pin is available for general purpose
I/O. See Section 3.0 “Device Configuration” for
more information.
4.3.2 FREQUENCY SELECT BITS (IRCF)
The output of the 16 MHz HFINTOSC is connected to
a divider and multiplexer (see Figure 4-1). The Internal
Oscillator Frequency Select bits (IRCF) of the
OSCCON register select the frequency output of the
internal oscillator:
•HFINTOSC
-16 MHz
- 8 MHz (default after Reset)
-4 MHz
-2 MHz
-1 MHz
-500 kHz
-250 kHz
•LFINTOSC
-31 kHz
There is no delay when switching between HFINTOSC
frequencies with the IRCF bits. This is because the
switch involves only a change to the frequency output
divider.
Start-up delay specifications are located in
Section 24.0 “Electrical Specifications”.
Note: Following any Reset, the IRCF<2:0> bits
of the OSCCON register are set to ‘110’
and the frequency selection is set to
8 MHz. The user can modify the IRCF bits
to select a different frequency.