PIC16LF18854 Datasheet, PDF (109/668 Pages) Microchip Technology – C Compiler Optimized RISC Architecture

PIC16(L)F18856/76
6.0 OSCILLATOR MODULE (WITH
FAIL-SAFE CLOCK MONITOR)
6.1 Overview
The oscillator module has a wide variety of 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 6-1 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 determine
the type of oscillator that will be used when the device
reset, including when it is first powered up.
The internal clock modes, LFINTOSC, HFINTOSC (set
at 1 MHz), or HFINTOSC (set at 32 MHz) can be set
through the RSTOSC bits.
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 500 kHz)
2. ECM – External Clock Medium Power mode
(500 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 4 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 INTOSC internal oscillator block produces low and
high-frequency clock sources, designated LFINTOSC
and HFINTOSC. (see Internal Oscillator Block,
Figure 6-1). A wide selection of device clock
frequencies may be derived from these clock sources.
 2016 Microchip Technology Inc.
Preliminary
DS40001824A-page 109