PIC16F684_07 Datasheet, PDF (21/192 Pages) Microchip Technology – 14-Pin, Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F684
3.0 OSCILLATOR MODULE (WITH
FAIL-SAFE CLOCK MONITOR)
3.1 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 3-1
illustrates a block diagram of the Oscillator module.
Clock sources can be configured from external
oscillators, quartz crystal resonators, ceramic resonators
and Resistor-Capacitor (RC) circuits. In addition, the
system clock source can be configured from one of two
internal oscillators, with a choice of speeds selectable via
software. Additional clock features include:
• Selectable system clock source between external
or internal 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.
The Oscillator module can be configured in one of eight
clock modes.
1. EC – External clock with I/O on OSC2/CLKOUT.
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) with
FOSC/4 output on OSC2/CLKOUT.
6. RCIO – External Resistor-Capacitor (RC) with
I/O on OSC2/CLKOUT.
7. INTOSC – Internal oscillator with FOSC/4 output
on OSC2 and I/O on OSC1/CLKIN.
8. INTOSCIO – Internal oscillator with I/O on
OSC1/CLKIN and OSC2/CLKOUT.
Clock Source modes are configured by the FOSC<2:0>
bits in the Configuration Word register (CONFIG). The
internal clock can be generated from two internal
oscillators. The HFINTOSC is a calibrated
high-frequency oscillator. The LFINTOSC is an
uncalibrated low-frequency oscillator.
FIGURE 3-1:
PIC^® MCU CLOCK SOURCE BLOCK DIAGRAM
OSC2
OSC1
External Oscillator
Sleep
Internal Oscillator
HFINTOSC
8 MHz
LFINTOSC
31 kHz
FOSC<2:0>
(Configuration Word Register)
SCS<0>
(OSCCON Register)
LP, XT, HS, RC, RCIO, EC
IRCF<2:0>
(OSCCON Register)
8 MHz
111
4 MHz
110
2 MHz
101
1 MHz
100
500 kHz
011
250 kHz
010
125 kHz
001
31 kHz
000
INTOSC
System Clock
(CPU and Peripherals)
Power-up Timer (PWRT)
Watchdog Timer (WDT)
Fail-Safe Clock Monitor (FSCM)
© 2007 Microchip Technology Inc.
DS41202F-page 19