PIC18F1XK22 Datasheet, PDF (15/388 Pages) Microchip Technology – 20-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC18F1XK22/LF1XK22
2.0 OSCILLATOR MODULE
2.1 Overview
The oscillator module has a variety of clock sources
and features that allow it to be used in a wide range of
applications, maximizing performance and minimizing
power consumption. Figure 2-1 illustrates a block
diagram of the oscillator module.
Key features of the oscillator module include:
• System Clocks
• System Clock Selection
- Primary External Oscillator
- Secondary External Oscillator
- Internal Oscillator
• Oscillator Start-up Timer
• System Clock Selection
• Clock Switching
• 4x Phase Lock Loop Frequency Multiplier
• CPU Clock Divider
• Two-Speed Start-up Mode
• Fail-Safe Clock Monitoring
2.2 System Clocks
The PIC18F1XK22/LF1XK22 can be operated in 13 dif-
ferent oscillator modes. The user can program these
using the available Configuration bits. In addition, clock
support functions such as Fail-Safe and two Start-up
can also be configured.
The available Primary oscillator options include:
• External Clock, low power (ECL)
• External Clock, medium power (ECM)
• External Clock, high power (ECH)
• External Clock, low power, CLKOUT function on
RA4/OSC2 (ECCLKOUTL)
• External Clock, medium power, CLKOUT function
on RA4/OSC2 (ECCLKOUTM)
• External Clock, high power, CLKOUT function on
RA4/OSC2 (ECCLKOUTH)
• External Crystal (XT)
• High-speed Crystal (HS)
• Low-power crystal (LP)
• External Resistor/Capacitor (EXTRC)
• External RC, CLKOUT function on RA4/OSC2
• 31.25 kHz – 16 MHz internal oscillator (INTOSC)
• 31.25 kHz – 16 MHz internal oscillator, CLKOUT
function on RA4/OSC2
Additionally, the 4xPLL may be enabled in hardware or
software (under certain conditions) for increased oscil-
lator speed.
2.3 System Clock Selection
The SCS bits of the OSCCON register select between
the following clock sources:
• Primary External Oscillator
• Secondary External Oscillator
• Internal Oscillator
Note:
The frequency of the system clock will be
referred to as FOSC throughout this
document.
TABLE 2-1: SYSTEM CLOCK SELECTION
Configuration
Selection
SCS <1:0>
1x
01
00
(Default after Reset)
System Clock
Internal Oscillator
Secondary External Oscillator
Oscillator defined by
FOSC<3:0>
The default state of the SCS bits sets the system clock
to be the oscillator defined by the FOSC bits of the
CONFIG1H Configuration register. The system clock
will always be defined by the FOSC bits until the SCS
bits are modified in software.
When the Internal Oscillator is selected as the system
clock, the IRCF bits of the OSCCON register and the
INTSRC bit of the OSCTUNE register will select either
the LFINTOSC or the HFINTOSC. The LFINTOSC is
selected when the IRCF<2:0> = 000 and the INTSRC
bit is clear. All other combinations of the IRCF bits and
the INTSRC bit will select the HFINTOSC as the
system clock.
2.4 Primary External Oscillator
The Primary External Oscillator’s mode of operation is
selected by setting the FOSC<3:0> bits of the
CONFIG1H Configuration register. The oscillator can
be set to the following modes:
• LP: Low-Power Crystal
• XT: Crystal/Ceramic Resonator
• HS: High-Speed Crystal Resonator
• RC: External RC Oscillator
• EC: External Clock
Additionally, the Primary External Oscillator may be
shut-down under firmware control to save power.
 2010 Microchip Technology Inc.
Preliminary
DS41365D-page 15