Datasheet
1997 Microchip Technology Inc. DS30390E-page 131
PIC16C7X
14.2 Oscillator Configurations
14.2.1 OSCILLATOR TYPES
The PIC16CXX 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
14.2.2 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 14-3). The
PIC16CXX 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 14-4).
FIGURE 14-3: CRYSTAL/CERAMIC
RESONATOR OPERATION
(HS, XT OR LP
OSC CONFIGURATION)
FIGURE 14-4: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
OSC CONFIGURATION)
Applicable Devices
72
73 73A 74 74A 76 77
C1
C2
XTAL
OSC2
Note1
OSC1
RF
SLEEP
To internal
logic
PIC16CXX
RS
See Table 14-1 and Table 14-2 for recommended values
of C1 and C2.
Note 1: A series resistor may be required for AT strip
cut crystals.
OSC1
OSC2
Open
Clock from
ext. system
PIC16CXX
TABLE 14-1: CERAMIC RESONATORS
TABLE 14-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
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 at bottom of page.
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.
Osc Type
Crystal
Freq
Cap. Range
C1
Cap. Range
C2
LP 32 kHz 33 pF 33 pF
200 kHz 15 pF 15 pF
XT 200 kHz 47-68 pF 47-68 pF
1 MHz 15 pF 15 pF
4 MHz 15 pF 15 pF
HS 4 MHz 15 pF 15 pF
8 MHz 15-33 pF 15-33 pF
20 MHz 15-33 pF 15-33 pF
These values are for design guidance only. See
notes at bottom of page.
Crystals Used
32 kHz Epson C-001R32.768K-A ± 20 PPM
200 kHz STD XTL 200.000KHz ± 20 PPM
1 MHz ECS ECS-10-13-1 ± 50 PPM
4 MHz ECS ECS-40-20-1 ± 50 PPM
8 MHz EPSON CA-301 8.000M-C ± 30 PPM
20 MHz EPSON CA-301 20.000M-C ± 30 PPM
Note 1: Recommended values of C1 and C2 are
identical to the ranges tested (Table 14-1).
2: Higher capacitance increases the stability
of oscillator but also increases the start-up
time.
3: Since each resonator/crystal has its own
characteristics, the user should consult the
resonator/crystal manufacturer for appropri-
ate values of external components.
4: Rs may be required in HS mode as well as
XT mode to avoid overdriving crystals with
low drive level specification.