PIC18LF24K Datasheet, PDF (34/594 Pages) –

PIC18(L)F26/45/46K40
4.0 OSCILLATOR MODULE (WITH
FAIL-SAFE CLOCK MONITOR)
4.1 Overview
The oscillator module has multiple clock sources and
selection features that allow it to be used in a wide
range of applications while maximizing performance
and minimizing power consumption. Figure 4-1
illustrates a block diagram of the oscillator module.
Clock sources can be supplied from external oscillators,
quartz-crystal resonators and ceramic resonators. In
addition, the system clock source can be supplied from
one of two internal oscillators and PLL circuits, with a
choice of speeds selectable via software. Additional
clock features include:
• Selectable system clock source between external
or internal sources via software.
• Fail-Safe Clock Monitor (FSCM) designed to
detect a failure of the external clock source (LP,
XT, HS, ECH, ECM, ECL) and switch
automatically to the internal oscillator.
• Oscillator Start-up Timer (OST) ensures stability
of crystal oscillator sources.
The RSTOSC bits of Configuration Word 1
(Register 3-1) determine the type of oscillator that will
be used when the device runs after Reset, including
when it is first powered up.
If an external clock source is selected, the FEXTOSC
bits of Configuration Word 1 must be used in
conjunction with the RSTOSC bits to select the
External Clock mode.
The external oscillator module can be configured in one
of the following clock modes, by setting the
FEXTOSC<2:0> bits of Configuration Word 1:
1. ECL – External Clock Low-Power mode
(below 100 kHz)
2. ECM – External Clock Medium Power mode
(100 kHz to 8 MHz)
3. ECH – External Clock High-Power mode
(above 8 MHz)
4. LP – 32 kHz Low-Power Crystal mode.
5. XT – Medium Gain Crystal or Ceramic Resonator
Oscillator mode (between 100 kHz and 8 MHz)
6. HS – High Gain Crystal or Ceramic Resonator
mode (above 4 MHz)
The ECH, ECM, and ECL Clock modes rely on an
external logic level signal as the device clock source.
The LP, XT, and HS Clock modes require an external
crystal or resonator to be connected to the device.
Each mode is optimized for a different frequency range.
The internal oscillator block produces low and
high-frequency clock sources, designated LFINTOSC
and HFINTOSC. (see Internal Oscillator Block,
Figure 4-1). Multiple device clock frequencies may be
derived from these clock sources.
 2016 Microchip Technology Inc.
Preliminary
DS40001816C-page 34