Datasheet

 2010-2012 Microchip Technology Inc. DS41414D-page 65
PIC16(L)F1946/47
5.2.1.5 TIMER1 Oscillator
The Timer1 Oscillator is a separate crystal oscillator
that is associated with the Timer1 peripheral. It is opti-
mized for timekeeping operations with a 32.768 kHz
crystal connected between the T1OSO and T1OSI
device pins.
The Timer1 Oscillator can be used as an alternate sys-
tem clock source and can be selected during run-time
using clock switching. Refer to Section 5.3 “Clock
Switching” for more information.
FIGURE 5-5: QUARTZ CRYSTAL
OPERATION (TIMER1
OSCILLATOR)
5.2.1.6 External RC Mode
The external Resistor-Capacitor (RC) modes support
the use of an external RC circuit. This allows the
designer maximum flexibility in frequency choice while
keeping costs to a minimum when clock accuracy is not
required.
The RC circuit connects to OSC1. OSC2/CLKOUT is
available for general purpose I/O or CLKOUT. The
function of the OSC2/CLKOUT pin is determined by the
C
LKOUTEN bit in Configuration Words.
Figure 5-6 shows the external RC mode connections.
FIGURE 5-6: EXTERNAL RC MODES
The RC oscillator frequency is a function of the supply
voltage, the resistor (R
EXT) and capacitor (CEXT) values
and the operating temperature. Other factors affecting
the oscillator frequency are:
• threshold voltage variation
• component tolerances
• packaging variations in capacitance
The user also needs to take into account variation due
to tolerance of external RC components used.
Note 1: Quartz crystal characteristics vary
according to type, package and
manufacturer. The user should consult the
manufacturer data sheets for specifications
and recommended application.
2: Always verify oscillator performance over
the V
DD and temperature range that is
expected for the application.
3: For oscillator design assistance, reference
the following Microchip Applications Notes:
• AN826, “Crystal Oscillator Basics and
Crystal Selection for rfPIC
®
and PIC
®
Devices” (DS00826)
• AN849, “Basic PIC
®
Oscillator Design”
(DS00849)
• AN943, “Practical PIC
®
Oscillator
Analysis and Design” (DS00943)
• AN949, “Making Your Oscillator Work”
(DS00949)
• TB097, “Interfacing a Micro Crystal
MS1V-T1K 32.768 kHz Tuning Fork
Crystal to a PIC16F690/SS” (DS91097)
• AN1288, “Design Practices for
Low-Power External Oscillators”
(DS01288)
C1
C2
32.768 kHz
T1OSI
To Internal
Logic
PIC
®
MCU
Crystal
T1OSO
Quartz
OSC2/CLKOUT
CEXT
REXT
PIC
®
MCU
OSC1/CLKIN
F
OSC/4 or
Internal
Clock
VDD
VSS
Recommended values: 10 k  REXT  100 k, <3V
3 k  R
EXT  100 k, 3-5V
C
EXT > 20 pF, 2-5V
Note 1: Output depends upon CLKOUTEN bit of the
Configuration Words.
I/O
(1)