Datasheet

 2009 Microchip Technology Inc. Preliminary DS41364D-page 69
PIC16F193X/LF193X
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.
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
4 x PLL
FOSC<2:0>
Oscillator
T1OSCEN
Enable
Oscillator
T1OSO
T1OSI
Clock Source Option
for other modules
OSC1
OSC2
Sleep
LP, XT, HS, RC, EC
T1OSC
CPU and
Postscaler
MUX
MUX
16 MHz
8 MHz
4 MHz
2 MHz
1 MHz
250 kHz
500 kHz
IRCF<3:0>
31 kHz
500 kHz
Source
Internal
Oscillator
Block
WDT, PWRT, Fail-Safe Clock Monitor
16 MHz
Internal Oscillator
(HFINTOSC)
Clock
Control
SCS<1:0>
HFPLL
31 kHz (LFINTOSC)
Two-Speed Start-up and other modules
Oscillator
31 kHz
Source
500 kHz
(MFINTOSC)
125 kHz
31.25 kHz
62.5 kHz
FOSC<2:0> = 100
Peripherals
Sleep
External
Timer1