RFPIC12F675K Datasheet, PDF (59/136 Pages) Microchip Technology – 20-Pin FLASH-Based 8-Bit CMOS Microcontroller with UHF ASK/FSK Transmitter

10.2 Oscillator Configurations
10.2.1 OSCILLATOR TYPES
The rfPIC12F675 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 PICmicro^TM
Mid-Range
Reference
Manual,
(DS33023)
10.2.2 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 10-1). The rfPIC12F675
oscillator 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 10-2).
FIGURE 10-1:
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
PIC12F629/675
Note 1: See Table 10-1 and Table 10-2 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 MΩ).
rfPIC12F675
FIGURE 10-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT, EC,
OR LP OSC
CONFIGURATION)
Clock from
External System
Open
OSC1
PIC12F629/675
OSC2⁽¹⁾
Note 1: Functions as GP4 in EC Osc mode.
TABLE 10-1: 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 10-2: 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.
 2003 Microchip Technology Inc.
Preliminary
DS70091A-page 57