PIC16F877-20L Datasheet, PDF (121/218 Pages) Microchip Technology – 28/40-Pin 8-Bit CMOS FLASH Microcontrollers

12.2 Oscillator Configurations
12.2.1 OSCILLATOR TYPES
The PIC16F87X can be operated in four different oscil-
lator modes. The user can program two configuration
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
12.2.2 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 12-1). The
PIC16F87X oscillator design requires the use of a par-
allel cut crystal. Use of a series cut crystal may give a
frequency out of the crystal manufacturers specifica-
tions. When in XT, LP or HS modes, the device can
have an external clock source to drive the OSC1/
CLKIN pin (Figure 12-2).
FIGURE 12-1:
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
PIC16F87X
Note 1: See Table 12-1 and Table 12-2 for recom-
mended 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.
PIC16F87X
FIGURE 12-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC16F87X
OSC2
TABLE 12-1: 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 12-2.
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.
 1998-2013 Microchip Technology Inc.
DS30292D-page 121