Datasheet

 2003 Microchip Technology Inc. DS39582B-page 145
PIC16F87XA
14.2 Oscillator Configurations
14.2.1 OSCILLATOR TYPES
The PIC16F87XA can be operated in four different
oscillator modes. The user can program two configura-
tion 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
14.2.2 CRYSTAL OSCILLATOR/CERAMIC
RESONATORS
In XT, LP or HS modes, a crystal or ceramic resonator
is connected to the OSC1/CLKI and OSC2/CLKO pins
to establish oscillation (Figure 14-1). The PIC16F87XA
oscillator design requires the use of a parallel cut crys-
tal. Use of a series cut crystal may give a frequency out
of the crystal manufacturer’s specifications. When in
XT, LP or HS modes, the device can have an external
clock source to drive the OSC1/CLKI pin (Figure 14-2).
FIGURE 14-1: CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP
OSC CONFIGURATION)
FIGURE 14-2: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC CONFIGURATION)
TABLE 14-1: CERAMIC RESONATORS
Note 1: See Table 14-1 and Table 14-2 for recommended
values of C1 and C2.
2: A series resistor (R
s
) 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
PIC16F87XA
R
s
(2)
Internal
Ranges Tested:
Mode Freq. OSC1 OSC2
XT 455 kHz
2.0 MHz
4.0 MHz
68-100 pF
15-68 pF
15-68 pF
68-100 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
These values are for design guidance only.
See notes following Table 14-2.
Resonators Used:
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%
16.0 MHz Murata Erie CSA16.00MX ± 0.5%
All resonators used did not have built-in capacitors.
OSC1
OSC2
Open
Clock from
Ext. System
PIC16F87XA