PIC16F870_13 Datasheet, PDF (89/172 Pages) Microchip Technology – 28/40-Pin, 8-Bit CMOS FLASH Microcontrollers

11.2 Oscillator Configurations
11.2.1 OSCILLATOR TYPES
The PIC16F870/871 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
• XT
• HS
• RC
Low Power Crystal
Crystal/Resonator
High Speed Crystal/Resonator
Resistor/Capacitor
11.2.2
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 11-1). The PIC16F870/
871 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/CLKI pin (Figure 11-2).
FIGURE 11-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP
OSC CONFIGURATION)
C1⁽¹⁾
OSC1
XTAL
C2⁽¹⁾
OSC2
R_s⁽²⁾
RF⁽³⁾
To
Internal
Logic
SLEEP
PIC16F870/871
Note 1:
2:
3:
See Table 11-1 and Table 11-2 for
recommended values of C1 and C2.
A series resistor (R_s) may be required for
AT strip cut crystals.
RF varies with the crystal chosen.
PIC16F870/871
FIGURE 11-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
OSC CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC16F870/871
OSC2
TABLE 11-1: CERAMIC RESONATORS
Ranges Tested:
Mode
Freq.
OSC1
OSC2
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 10 - 68 pF
16.0 MHz 10 - 22 pF 10 - 22 pF
These values are for design guidance only.
See notes following Table 11-2.
Resonators Used:
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%
16.0 MHz Murata Erie CSA16.00MX  0.5%
All resonators used did not have built-in capacitors.
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DS30569C-page 89