PIC16LC925T-I/CL View Datasheet(PDF) - Microchip Technology
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PIC16LC925T-I/CL Datasheet PDF : 182 Pages
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12.2 Oscillator Configurations
12.2.1 OSCILLATOR TYPES
The PIC16CXXX 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
PIC16CXXX 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)
OSC1
C1
XTAL
OSC2
RS
C2 (Note 1)
To Internal
Logic
RF
SLEEP
PIC16CXXX
See Table 12-1 and Table 12-2 for recommended values
of C1 and C2.
Note 1: A series resistor may be required for AT strip
cut crystals.
FIGURE 12-2:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR
LP OSC
CONFIGURATION)
Clock from
Ext. System
Open
OSC1
PIC16CXXX
OSC2
PIC16C925/926
TABLE 12-1: CERAMIC RESONATORS
Ranges Tested:
Mode
Freq.
C1
C2
455 kHz 68 - 100 pF 68 - 100 pF
XT
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
These values are for design guidance only.
See notes following Table 12-2.
TABLE 12-2: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Osc Type
Crystal
Freq.
Cap. Range
C1
Cap.
Range
C2
32 kHz
LP
200 kHz
33 pF
15 pF
33 pF
15 pF
200 kHz 47-68 pF
47-68 pF
XT
1 MHz
15 pF
15 pF
4 MHz
15 pF
15 pF
4 MHz
15 pF
15 pF
HS
8 MHz
15-33 pF
15-33 pF
These values are for design guidance only.
See notes following this table.
Note 1: Recommended ranges of C1 and C2 are
depicted in Table 12-1.
2: Higher capacitance increases the stability
of the 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
appropriate values of external compo-
nents.
4: Rs may be required in HS mode, as well
as XT mode, to avoid overdriving crystals
with low drive level specification.
2001 Microchip Technology Inc.
Preliminary
DS39544A-page 99
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