PIC16F676-I Datasheet, PDF (57/132 Pages) Microchip Technology – 14-Pin, Flash-Based 8-Bit CMOS Microcontrollers

9.2 Oscillator Configurations
9.2.1 OSCILLATOR TYPES
The PIC16F630/676 can be operated in eight different
Oscillator Option modes. The user can program three
Configuration bits (FOSC2 through FOSC0) to select
one of these eight modes:
• LP
Low-Power Crystal
• XT
Crystal/Resonator
• HS
High Speed Crystal/Resonator
• RC External Resistor/Capacitor (2 modes)
• INTOSC Internal Oscillator (2 modes)
• EC
External Clock In
Note:
Additional information on oscillator config-
urations is available in the PIC^® Mid-Range
Reference Manual, (DS33023).
9.2.2
CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT, LP or HS modes a crystal or ceramic resonator
is connected to the OSC1 and OSC2 pins to establish
oscillation (see Figure 9-1). The PIC16F630/676 oscil-
lator design requires the use of a parallel cut crystal.
Use of a series cut crystal may yield a frequency
outside of the crystal manufacturers specifications.
When in XT, LP or HS modes, the device can have an
external clock source to drive the OSC1 pin (see
Figure 9-2).
FIGURE 9-1:
CRYSTAL OPERATION (OR
CERAMIC RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
C2⁽¹⁾
OSC2
RS⁽²⁾
RF⁽³⁾
To Internal
Logic
Sleep
PIC16F630/676
Note
1: See Table 9-1 and Table 9-2 for recommended
values of C1 and C2.
2: A series resistor may be required for AT strip cut
crystals.
3: RF varies with the Oscillator mode selected
(Approx. value = 10 M
PIC16F630/676
FIGURE 9-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT, EC,
OR LP OSC
CONFIGURATION)
Clock from
External System
Open
OSC1
PIC16F630/676
OSC2⁽¹⁾
Note 1: Functions as RA4 in EC Osc mode.
TABLE 9-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Ranges Characterized:
Mode
Freq
OSC1(C1) OSC2(C2)
XT
455 kHz
68-100 pF
68-100 pF
2.0 MHz
15-68 pF
15-68 pF
4.0 MHz
15-68 pF
15-68 pF
HS 8.0 MHz
10-68 pF
16.0 MHz 10-22 pF
10-68 pF
10-22 pF
Note 1: Higher capacitance increases the stability
of the oscillator but also increases the
start-up time. These values are for design
guidance only. Since each resonator has
its own characteristics, the user should
consult the resonator manufacturer for
appropriate values of external
components.
TABLE 9-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Mode
Freq
OSC1(C1) OSC2(C2)
LP
32 kHz 68-100 pF 68-100 pF
XT
100 kHz 68-150 pF 150-200 pF
2 MHz
15-30 pF
15-30 pF
4 MHz
15-30 pF
15-30 pF
HS
8 MHz
15-30 pF
15-30 pF
10 MHz
15-30 pF
15-30 pF
20 MHz
15-30 pF
15-30 pF
Note 1: Higher capacitance increases the stability
of the oscillator but also increases the
start-up time. These values are for design
guidance only. Rs may be required in HS
mode as well as XT mode to avoid
overdriving crystals with low drive level
specification. Since each crystal has its
own characteristics, the user should
consult the crystal manufacturer for
appropriate values of external
components.
 2010 Microchip Technology Inc.
DS40039F-page 57