Datasheet

 1996-2013 Microchip Technology Inc. Preliminary DS40143E-page 33
PIC16C55X
6.2 Oscillator Configurations
6.2.1 OSCILLATOR TYPES
The PIC16C55X can be operated in four different
oscillator options. The user can program two
configuration bits (FOSC1 and FOSC0) to select one of
these four modes:
• LP Low Power Crystal
• XT Crystal/Resonator
• HS High Speed Crystal/Resonator
• RC Resistor/Capacitor
6.2.2 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 6-1). The PIC16C55X 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 6-2).
FIGURE 6-1: CRYSTAL OPERATION 
(OR CERAMIC
RESONATOR) (HS, XT OR
LP OSC
CONFIGURATION)
FIGURE 6-2: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
TABLE 6-1: CAPACITOR SELECTION FOR
CERAMIC RESONATORS
(PRELIMINARY)
TABLE 6-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
(PRELIMINARY)
Note 1: A series resistor may be required for AT strip cut
crystals.
2: See Table 6-1 and Table 6-2 for recommended val-
ues of C1 and C2.
C1
C2
XTAL
OSC2
RS
OSC1
RF
SLEEP
To internal logic
PIC16C55X
Note 1
Clock from
ext. system
PIC16C55X
OSC1
OSC2
Open
Ranges Characterized:
Mode Freq OSC1(C1) OSC2(C2)
XT 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
HS 8.0 MHz
16.0 MHz
10 - 68 pF
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 with the resonator manufacturer for
appropriate values of external compo-
nents.
Mode Freq OSC1(C1) OSC2(C2)
LP 32 kHz
200 kHz
68 - 100 pF
15 - 30 pF
68 - 100 pF
15 - 30 pF
XT 100 kHz
2 MHz
4 MHz
68 - 150 pF
15 - 30 pF
15 - 30 pF
150 - 200 pF
15 - 30 pF
15 - 30 pF
HS 8 MHz
10 MHz
20 MHz
15 - 30 pF
15 - 30 pF
15 - 30 pF
15 - 30 pF
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 over-
driving crystals with low-drive level specifi-
cation. Since each crystal has its own
characteristics, the user should consult
with the crystal manufacturer for appropri-
ate values of external components.