PIC16LF1904 Datasheet, PDF (60/288 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers with LCD Driver and nanoWatt XLP Technology

PIC16LF1904/6/7
6.2.1.2 Secondary Oscillator
The secondary 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 T1CKI/T1OSO and
T1OSI device pins.
The secondary oscillator can be used as an alternate
system clock source and can be selected during
run-time using clock switching. Refer to Section 6.3
“Clock Switching” for more information.
FIGURE 6-3:
QUARTZ CRYSTAL
OPERATION
(SECONDARY
OSCILLATOR)
PIC^® MCU
T1CKI/T1OSO
C1
32.768 kHz
Quartz
Crystal
To Internal
Logic
C2
T1OSI
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 VDD 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)
6.2.2 INTERNAL CLOCK SOURCES
The device may be configured to use the internal oscil-
lator block as the system clock by performing one of the
following actions:
• Program the FOSC<1:0> bits in Configuration
Word 1 to select the INTOSC clock source, which
will be used as the default system clock upon a
device Reset.
• Write the SCS<1:0> bits in the OSCCON register
to switch the system clock source to the internal
oscillator during run-time. See Section 6.3
“Clock Switching”for more information.
In INTOSC mode, CLKIN is available for general
purpose I/O. CLKOUT is available for general purpose
I/O or CLKOUT.
The function of the CLKOUT pin is determined by the
state of the CLKOUTEN bit in Configuration Word 1.
The internal oscillator block has two independent
oscillators that provides the internal system clock
source.
1. The HFINTOSC (High-Frequency Internal
Oscillator) is factory calibrated and operates at
16 MHz.
2. The LFINTOSC (Low-Frequency Internal
Oscillator) is uncalibrated and operates at
31 kHz.
6.2.2.1 HFINTOSC
The High-Frequency Internal Oscillator (HFINTOSC) is
a factory calibrated 16 MHz internal clock source.
The output of the HFINTOSC connects to a postscaler
and multiplexer (see Figure 6-1). The frequency derived
from the HFINTOSC can be selected via software using
the IRCF<3:0> bits of the OSCCON register. See
Section 6.2.2.4 “Internal Oscillator Clock Switch
Timing” for more information.
The HFINTOSC is enabled by:
• Configure the IRCF<3:0> bits of the OSCCON
register for the desired HF frequency, and
• FOSC<1:0> = 11, or
• Set the System Clock Source (SCS) bits of the
OSCCON register to ‘1x’.
The High-Frequency Internal Oscillator Ready bit
(HFIOFR) of the OSCSTAT register indicates when the
HFINTOSC is running and can be utilized.
The High-Frequency Internal Oscillator Status Stable
bit (HFIOFS) of the OSCSTAT register indicates when
the HFINTOSC is running within 0.5% of its final value.
DS41569A-page 60
Preliminary
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