
2001 Microchip Technology Inc.
DS30292C-page 121
PIC16F87X
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
Low Power Crystal
XT
Crystal/Resonator
HS
High Speed Crystal/Resonator
RC
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
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/
FIGURE 12-1:
CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP
OSC CONFIGURATION)
FIGURE 12-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
TABLE 12-1:
CERAMIC RESONATORS
mended 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
PIC16F87X
Rs
(2)
Internal
Ranges Tested:
Mode
Freq.
OSC1
OSC2
XT
455 kHz
2.0 MHz
4.0 MHz
68 - 100 pF
15 - 68 pF
68 - 100 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.
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.
OSC1
OSC2
Open
Clock from
Ext. System
PIC16F87X