PIC16F639 Microchip Technology Inc., PIC16F639 Datasheet - Page 37

• Manufacturer Part Number: PIC16F639
• Description: 8/14-pin Flash-based, 8-bit Cmos Microcontrollers With Nanowatt Technology
• Manufacturer: Microchip Technology Inc.

3.0
3.1
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
• Two-Speed Start-up mode, which minimizes
• Fail-Safe Clock Monitor (FSCM) designed to
FIGURE 3-1:
© 2007 Microchip Technology Inc.
or internal via software.
latency between external oscillator start-up and
code execution.
detect a failure of the external clock source (LP,
XT, HS, EC or RC modes) and switch
automatically to the internal oscillator.
OSC2
OSC1
OSCILLATOR MODULE (WITH
FAIL-SAFE CLOCK MONITOR)
Overview
External Oscillator
Internal Oscillator
HFINTOSC
LFINTOSC
31 kHz
8 MHz
PIC
®
MCU CLOCK SOURCE BLOCK DIAGRAM
Sleep
500 kHz
250 kHz
125 kHz
31 kHz
8 MHz
4 MHz
2 MHz
1 MHz
PIC12F635/PIC16F636/639
(OSCCON Register)
IRCF<2:0>
111
110
101
100
011
010
001
000
The Oscillator module can be configured in one of eight
clock modes.
1.
2.
3.
4.
5.
6.
7.
8.
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.
high-frequency oscillator. The LFINTOSC is an
uncalibrated low-frequency oscillator.
LP, XT, HS, RC, RCIO, EC
EC – External clock with I/O on OSC2/CLKOUT.
LP – 32 kHz Low-Power Crystal mode.
XT – Medium Gain Crystal or Ceramic
Resonator Oscillator mode.
HS – High Gain Crystal or Ceramic Resonator
mode.
RC – External Resistor-Capacitor (RC) with
F
RCIO – External Resistor-Capacitor (RC) with
I/O on OSC2/CLKOUT.
INTOSC – Internal oscillator with F
on OSC2 and I/O on OSC1/CLKIN.
INTOSCIO – Internal oscillator with I/O on
OSC1/CLKIN and OSC2/CLKOUT.
OSC
/4 output on OSC2/CLKOUT.
The
Power-up Timer (PWRT)
Watchdog Timer (WDT)
Fail-Safe Clock Monitor (FSCM)
INTOSC
(Configuration Word Register)
HFINTOSC
(OSCCON Register)
FOSC<2:0>
SCS<0>
(CPU and Peripherals)
is
DS41232D-page 35
System Clock
OSC
a
/4 output
calibrated