PIC16F1946 Datasheet, PDF (61/440 Pages) Microchip Technology – 64-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC16F/LF1946/47
5.0 OSCILLATOR MODULE (WITH
FAIL-SAFE CLOCK MONITOR)
5.1 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 perfor-
mance and minimizing power consumption. Figure 5-1
illustrates a block diagram of the oscillator module.
Clock sources can be supplied from external oscillators,
quartz crystal resonators, ceramic resonators and
Resistor-Capacitor (RC) circuits. 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.
• Two-Speed Start-up mode, which minimizes
latency between external oscillator start-up and
code execution.
• Fail-Safe Clock Monitor (FSCM) designed to
detect a failure of the external clock source (LP,
XT, HS, EC or RC modes) and switch
automatically to the internal oscillator.
• Oscillator Start-up Timer (OST) ensures stability
of crystal oscillator sources
The oscillator module can be configured in one of six
clock modes.
1. EC – External clock (ECL, ECM, ECH. See
Section 5.2.1.1 “EC Mode”).
2. LP – 32 kHz Low-Power Crystal mode.
3. XT – Medium Gain Crystal or Ceramic Resonator
Oscillator mode.
4. HS – High Gain Crystal or Ceramic Resonator
mode.
5. RC – External Resistor-Capacitor (RC).
6. INTOSC – Internal oscillator.
Clock Source modes are selected by the FOSC<2:0>
bits in the Configuration Word 1. The FOSC bits
determine the type of oscillator that will be used when
the device is first powered.
The EC clock mode relies 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 RC clock mode
requires an external resistor and capacitor to set the
oscillator frequency.
The INTOSC internal oscillator block produces low,
medium, and high frequency clock sources, designated
LFINTOSC, MFINTOSC and HFINTOSC. (see Internal
Oscillator Block, Figure 5-1). A wide selection of device
clock frequencies may be derived from these three
clock sources.
FIGURE 5-1:
SIMPLIFIED PIC^® MCU CLOCK SOURCE BLOCK DIAGRAM
OSC2
OSC1
T1OSO
T1OSI
External
Oscillator
Sleep
Oscillator ^Timer1
T1OSCEN
Enable
Oscillator
Internal
Oscillator
Block
HFPLL
500 kHz
Source
31 kHz
Source
16 MHz
(HFINTOSC)
500 kHz
(MFINTOSC)
LP, XT, HS, RC, EC
4 x PLL
FOSC<2:0> = 100
T1OSC
Sleep
CPU and
Peripherals
IRCF<3:0>
16 MHz
8 MHz
4 MHz
2 MHz
1 MHz
500 kHz
250 kHz
125 kHz
62.5 kHz
31.25 kHz
31 kHz
Internal Oscillator
Clock
Control
FOSC<2:0> SCS<1:0>
Clock Source Option
for other modules
31 kHz (LFINTOSC)
WDT, PWRT, Fail-Safe Clock Monitor
Two-Speed Start-up and other modules
 2010 Microchip Technology Inc.
Preliminary
DS41414A-page 59