PIC16CR54C
7.2
Oscillator Configurations
OSCILLATOR TYPES
FIGURE 7-3: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
7.2.1
OSC CONFIGURATION)
PIC16CR54Cs can be operated in four different
oscillator modes. The user can program two
configuration bits (FOSC1:FOSC0) to select one of
these four modes:
OSC1
OSC2
Clock from
ext. system
PIC16CR54C
Open
• LP:
• XT:
• HS:
• RC:
Low Power Crystal
Crystal/Resonator
High Speed Crystal/Resonator
Resistor/Capacitor
TABLE 7-1:
CAPACITOR SELECTION
FOR CERAMIC RESONATORS
- PIC16CR54C
7.2.2
CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
Osc
Resonator Cap. Range Cap. Range
Type
Freq
C1
C2
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 7-2). The
PIC16CR54C 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 drive the
OSC1/CLKIN pin (Figure 7-3).
XT
455 kHz
2.0 MHz
4.0 MHz
68-100 pF
15-33 pF
10-22 pF
68-100 pF
15-33 pF
10-22 pF
HS
8.0 MHz
16.0 MHz
10-22 pF
10 pF
10-22 pF
10 pF
These values are for design guidance only. Since
each resonator has its own characteristics, the user
should consult the resonator manufacturer for
appropriate values of external components.
FIGURE 7-2: CRYSTAL OPERATION
(OR CERAMIC RESONATOR)
(HS, XT OR LP OSC
TABLE 7-2:
CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
- PIC16CR54C
CONFIGURATION)
Osc
Type
Resonator Cap.Range Cap. Range
(1)
C1
OSC1
Freq
C1
C2
PIC16CR54C
(1)
LP
XT
32 kHz
15 pF
15 pF
SLEEP
100 kHz
200 kHz
455 kHz
1 MHz
15-30 pF
15-30 pF
15-30 pF
15-30 pF
15 pF
200-300 pF
100-200 pF
15-100 pF
15-30 pF
15 pF
XTAL
(3)
RF
To internal
logic
OSC2
(2)
RS
(1)
C2
2 MHz
4 MHz
15 pF
15 pF
Note 1: See Capacitor Selection tables for
recommended values of C1 and C2.
2: A series resistor (RS) may be required for
AT strip cut crystals.
HS
4 MHz
8 MHz
20 MHz
15 pF
15 pF
15 pF
15 pF
15 pF
15 pF
3: RF varies with the crystal chosen (approx.
value = 10 MΩ).
Note 1: For VDD > 4.5V, C1 = C2 ≈ 30 pF is
recommended.
These values are for design guidance only. Rs may
be required in HS mode as well as XT mode to avoid
overdriving crystals with low drive level specification.
Since each crystal has its own characteristics, the
user should consult the crystal manufacturer for
appropriate values of external components.
Note:
If you change from this device to
another device, please verify oscillator
characteristics in your application.
DS40191A-page 26
Preliminary
1998 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
