Datasheet
PIC12C5XX
DS40139E-page 36 1999 Microchip Technology Inc.
8.2 Oscillator Configurations
8.2.1 OSCILLATOR TYPES
The PIC12C5XX can be operated in four different
oscillator modes. The user can program two
configuration bits (FOSC1:FOSC0) to select one of
these four modes:
•LP: Low Power Crystal
• XT: Crystal/Resonator
• INTRC: Internal 4 MHz Oscillator
• EXTRC: External Resistor/Capacitor
8.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT or LP modes, a crystal or ceramic resonator is
connected to the GP5/OSC1/CLKIN and GP4/OSC2
pins to establish oscillation (Figure 8-2). The
PIC12C5XX 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 or LP modes, the device
can have an external clock source drive the GP5/
OSC1/CLKIN pin (Figure 8-3).
FIGURE 8-2: CRYSTAL OPERATION (OR
CERAMIC RESONATOR) (XT
OR LP OSC
CONFIGURATION)
FIGURE 8-3: EXTERNAL CLOCK INPUT
OPERATION (XT OR LP OSC
CONFIGURATION)
Note 1: See Capacitor Selection tables for
recommended values of C1 and C2.
2: A series resistor (RS) may be required for
AT strip cut crystals.
3: RF approximate value = 10 MΩ.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
SLEEP
To internal
logic
RS
(2)
PIC12C5XX
Clock from
ext. system
OSC1
OSC2
Open
PIC12C5XX
TABLE 8-1: CAPACITOR SELECTION
FOR CERAMIC RESONATORS
- PIC12C5XX
TABLE 8-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR -
PIC12C5XX
Osc
Type
Resonator
Freq
Cap. Range
C1
Cap. Range
C2
XT 4.0 MHz 30 pF 30 pF
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.
Osc
Type
Resonator
Freq
Cap.Range
C1
Cap. Range
C2
LP 32 kHz
(1)
15 pF 15 pF
XT 200 kHz
1 MHz
4 MHz
47-68 pF
15 pF
15 pF
47-68 pF
15 pF
15 pF
Note 1: For V
DD > 4.5V, C1 = C2 ≈ 30 pF is
recommended.
These values are for design guidance only. Rs may
be required to avoid overdriving crystals with low
drive level specification. Since each crystal has its
own characteristics, the user should consult the crys-
tal manufacturer for appropriate values of external
components.