Datasheet

 1996 Microchip Technology Inc. DS30430B-page 39
PIC16F8X
8.2 Oscillator Confi
gurations
8.2.1 OSCILLATOR TYPES
The PIC16F8X can be operated in four different
oscillator modes. 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
8.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT, LP or HS modes a crystal or ceramic resonator
is connected to the OSC1/CLKIN and OSC2/CLKOUT
pins to establish oscillation (Figure 8-3).
FIGURE 8-3: CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP OSC
CONFIGURATION)
The PIC16F8X 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/CLKIN pin (Figure 8-4).
FIGURE 8-4: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
OSC CONFIGURATION)
Note1: See Table 8-1 for recommended values of
C1 and C2.
2: A series resistor (RS) may be required for
AT strip cut crystals.
3: RF varies with the crystal chosen.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
SLEEP
To
logic
PIC16FXX
RS
(2)
internal
OSC1
OSC2
Open
Clock from
ext. system
PIC16FXX
TABLE 8-1: PIC16F83/CR83/F84/CR84
CAPACITOR SELECTION
FOR CERAMIC RESONATORS
Ranges Tested:
Mode Freq OSC1/C1 OSC2/C2
XT 455 kHz
2.0 MHz
4.0 MHz
47 - 100 pF
15 - 33 pF
15 - 33 pF
47 - 100 pF
15 - 33 pF
15 - 33 pF
HS 8.0 MHz
10.0 MHz
15 - 33 pF
15 - 33 pF
15 - 33 pF
15 - 33 pF
Note: Recommended values of C1 and C2 are identical
to the ranges tested table.
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 the
appropriate values of external components.
Resonators Tested:
455 kHz Panasonic EFO-A455K04B ± 0.3%
2.0 MHz Murata Erie CSA2.00MG ± 0.5%
4.0 MHz Murata Erie CSA4.00MG ± 0.5%
8.0 MHz Murata Erie CSA8.00MT ± 0.5%
10.0 MHz Murata Erie CSA10.00MTZ ± 0.5%
None of the resonators had built-in capacitors.