PIC16F684
3.0
3.1
CLOCK SOURCES
Overview
The PIC16F684 can be configured in one of eight clock
modes.
1.
2.
3.
4.
5.
6.
7.
8.
EC – External clock with I/O on RA4.
LP – Low gain Crystal or Ceramic Resonator
Oscillator mode.
XT – Medium gain Crystal or Ceramic Resona-
tor Oscillator mode.
HS – High gain Crystal or Ceramic Resonator
mode.
RC – External Resistor-Capacitor (RC) with
F
OSC
/4 output on RA4.
RCIO – External Resistor-Capacitor with I/O on
RA4.
INTRC – Internal oscillator with F
OSC
/4 output
on RA4 and I/O on RA5.
INTRCIO – Internal oscillator with I/O on RA4
and RA5.
The PIC16F684 has a wide variety of clock sources
and selection features to allow it to be used in a wide
range of applications while maximizing performance
and minimizing power consumption. Figure 3-1
illustrates a block diagram of the PIC16F684 clock
sources.
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 Clock Start-up mode, which mini-
mizes 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 to the
internal oscillator.
Clock source modes are configured by the FOSC<2:0>
bits in the Configuration Word register (see
The
internal clock can be generated by two oscillators. The
HFINTOSC is a high-frequency calibrated oscillator.
The LFINTOSC is a low-frequency uncalibrated
oscillator.
FIGURE 3-1:
PIC16F684 CLOCK SOURCE BLOCK DIAGRAM
FOSC<2:0>
(Configuration Word)
SCS
(OSCCON<0>)
External Oscillator
OSC2
Sleep
OSC1
IRCF<2:0>
(OSCCON<6:4>)
8 MHz
Internal Oscillator
4 MHz
2 MHz
Postscaler
101
100
500 kHz
250 kHz
125 kHz
LFINTOSC
31 kHz
31 kHz
011
010
001
000
MUX
1 MHz
HFINTOSC
8 MHz
111
110
LP, XT, HS, RC, RCIO, EC
MUX
System Clock
(CPU and Peripherals)
Power-up Timer (PWRT)
Watchdog Timer (WDT)
Fail-Safe Clock Monitor (FSCM)
2004 Microchip Technology Inc.
Preliminary
DS41202C-page 19
MICROCHIP [ MICROCHIP TECHNOLOGY ]
