Datasheet

 2001-2013 Microchip Technology Inc. DS39598F-page 33
PIC16F818/819
4.0 OSCILLATOR
CONFIGURATIONS
4.1 Oscillator Types
The PIC16F818/819 can be operated in eight different
oscillator modes. The user can program three configu-
ration bits (FOSC2:FOSC0) to select one of these eight
modes (modes 5-8 are new PIC16 oscillator
configurations):
1. LP Low-Power Crystal
2. XT Crystal/Resonator
3. HS High-Speed Crystal/Resonator
4. RC External Resistor/Capacitor with
F
OSC/4 output on RA6
5. RCIO External Resistor/Capacitor with
I/O on RA6
6. INTIO1 Internal Oscillator with F
OSC/4
output on RA6 and I/O on RA7
7. INTIO2 Internal Oscillator with I/O on RA6
and RA7
8. ECIO External Clock with I/O on RA6
4.2 Crystal Oscillator/Ceramic
Resonators
In XT, LP or HS modes, a crystal or ceramic resonator
is connected to the OSC1/CLKI and OSC2/CLKO pins
to establish oscillation (see Figure 4-1 and Figure 4-2).
The PIC16F818/819 oscillator design requires the use
of a parallel cut crystal. Use of a series cut crystal may
give a frequency out of the crystal manufacturer’s
specifications.
FIGURE 4-1: CRYSTAL OPERATION
(HS, XT OR LP OSC
CONFIGURATION)
TABLE 4-1: CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR (FOR
DESIGN GUIDANCE ONLY)
Note 1: See Table 4-1 for typical values of C1 and C2.
2: A series resistor (R
S) may be required for AT
strip cut crystals.
3: R
F varies with the crystal chosen (typically
between 2 M to 10 M.
C1
(1)
C2
(1)
XTAL
OSC2
R
S
(2)
OSC1
RF
(3)
Sleep
To Internal
Logic
PIC16F818/819
Osc Type
Crystal
Freq
Typical Capacitor Values
Tested:
C1 C2
LP 32 kHz 33 pF 33 pF
200 kHz 15 pF 15 pF
XT 200 kHz 56 pF 56 pF
1 MHz 15 pF 15 pF
4 MHz 15 pF 15 pF
HS 4 MHz 15 pF 15 pF
8 MHz 15 pF 15 pF
20 MHz 15 pF 15 pF
Capacitor values are for design guidance only.
These capacitors were tested with the crystals listed
below for basic start-up and operation. These values
were not optimized.
Different capacitor values may be required to produce
acceptable oscillator operation. The user should test
the performance of the oscillator over the expected
V
DD and temperature range for the application.
See the notes following this table for additional
information.
Note 1: Higher capacitance increases the stability
of the oscillator but also increases the
start-up time.
2: Since each crystal has its own character-
istics, the user should consult the crystal
manufacturer for appropriate values of
external components.
3: R
S may be required in HS mode, as well
as XT mode, to avoid overdriving crystals
with low drive level specification.
4: Always verify oscillator performance over
the V
DD and temperature range that is
expected for the application.