PIC16F627A_05 Datasheet, PDF (99/180 Pages) Microchip Technology – Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC16F627A/628A/648A
14.2 Oscillator Configurations
14.2.1 OSCILLATOR TYPES
The PIC16F627A/628A/648A can be operated in eight
different oscillator options. 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 Precision Oscillator (2 modes)
• EC
External Clock In
14.2.2 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 (Figure 14-1). The PIC16F627A/628A/648A
oscillator design requires the use of a parallel cut
crystal. Use of a series cut crystal may give a frequency
out 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 (Figure 14-4).
FIGURE 14-1:
CRYSTAL OPERATION
(OR CERAMIC RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)
C1⁽²⁾
OSC1
XTAL
C2⁽²⁾
OSC2
RS⁽¹⁾
RF
Sleep
FOSC
PIC16F627A/628A/648A
Note
1: A series resistor may be required for AT strip cut
crystals.
2: See Table 14-1 and Table 14-2 for recommended
values of C1 and C2.
TABLE 14-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Mode
Freq
OSC1(C1) OSC2(C2)
XT
HS
Note:
455 kHz
2.0 MHz
4.0 MHz
22-100 pF
15-68 pF
15-68 pF
22-100 pF
15-68 pF
15-68 pF
8.0 MHz
16.0 MHz
10-68 pF
10-22 pF
10-68 pF
10-22 pF
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 compo-
nents.
TABLE 14-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Mode
Freq
OSC1(C1) OSC2(C2)
LP
XT
HS
Note:
32 kHz
200 kHz
15-30 pF
0-15 pF
15-30 pF
0-15 pF
100 kHz
2 MHz
4 MHz
68-150 pF
15-30 pF
15-30 pF
150-200 pF
15-30 pF
15-30 pF
8 MHz
10 MHz
20 MHz
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15-30 pF
Higher capacitance increases the stability
of the oscillator, but also increases the
start-up time. These values are for design
guidance only. A series resistor (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 manufac-
turer for appropriate values of external
components.
© 2005 Microchip Technology Inc.
DS40044D-page 97