Datasheet

PIC16C505
DS40192D-page 28  1999-2012 Microchip Technology Inc.
7.2 Oscillator Configurations
7.2.1 OSCILLATOR TYPES
The PIC16C505 can be operated in four different
oscillator modes. The user can program three
configuration bits (FOSC<2:0>) to select one of these
four modes:
• LP: Low Power Crystal
• XT: Crystal/Resonator
• HS: High Speed Crystal/Resonator
• INTRC: Internal 4 MHz Oscillator
• EXTRC: External Resistor/Capacitor
7.2.2 CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In HS, XT or LP modes, a crystal or ceramic resonator
is connected to the RB5/OSC1/CLKIN and RB4/
OSC2/CLKOUT pins to establish oscillation
(Figure 7-1). The PIC16C505 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 HS, XT
or LP modes, the device can have an external clock
source drive the RB5/OSC1/CLKIN pin (Figure 7-2).
FIGURE 7-1: CRYSTAL OPERATION (OR
CERAMIC RESONATOR)
(HS, XT OR LP OSC
CONFIGURATION)
FIGURE 7-2: EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
OSC CONFIGURATION)
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.
3: RF approx. value = 10 M.
C1
(1)
C2
(1)
XTAL
OSC2
OSC1
RF
(3)
SLEEP
To internal
logic
RS
(2)
PIC16C505
Clock from
ext. system
OSC1
OSC2
PIC16C505
Open
TABLE 7-1: CAPACITOR SELECTION
FOR CERAMIC RESONATORS
- PIC16C505
TABLE 7-2: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR -
PIC16C505
Osc
Type
Resonator
Freq
Cap. Range
C1
Cap. Range
C2
XT 4.0 MHz 30 pF 30 pF
HS 16 MHz 10-47 pF 10-47 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.
Osc
Type
Resonator
Freq
Cap.Range
C1
Cap. Range
C2
LP 32 kHz
(1)
15 pF 15 pF
XT 200 kHz
1 MHz
4 MHz
47-68 pF
15 pF
15 pF
47-68 pF
15 pF
15 pF
HS 20 MHz 15-47 pF 15-47 pF
Note 1: For V
DD > 4.5V, C1 = C2  30 pF is
recommended.
These values are for design guidance only. Rs may
be required to avoid overdriving crystals with low
drive level specification. Since each crystal has its
own characteristics, the user should consult the crys-
tal manufacturer for appropriate values of external
components.