PIC18F-LF1XK50 Datasheet, PDF (15/420 Pages) Microchip Technology – 20-Pin USB Flash Microcontrollers

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 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
• USB Operation
- Low Speed
- Full Speed
• Two-Speed Start-up Mode
• Fail-Safe Clock Monitoring
PIC18F/LF1XK50
2.2 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>
System Clock
1x
Internal Oscillator
01
Secondary External Oscillator
00
Oscillator defined by
(Default after Reset) 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.
2.3 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
DS41350E-page 15