2004 Microchip Technology Inc.
DS30498C-page 33
PIC16F7X7
4.0
OSCILLATOR
CONFIGURATIONS
4.1
Oscillator Types
The PIC16F7X7 can be operated in eight different oscil-
lator modes. The user can program three configuration
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
FOSC/4 output on RA6
5.
RCIO
External Resistor/Capacitor with
I/O on RA6
6.
INTIO1 Internal Oscillator with FOSC/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
The PIC16F7X7 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 (RS) may be required for AT
strip cut crystals.
3: RF varies with the crystal chosen (typically
between 2 M
to 10 M).
C1(1)
C2(1)
XTAL
OSC2
RS(2)
OSC1
RF(3)
Sleep
To Internal
Logic
PIC16F7X7
Osc Type
Crystal
Freq
Typical Capacitor Values
Tested:
C1
C2
LP
32 kHz
33 pF
200 kHz
15 pF
XT
200 kHz
56 pF
1 MHz
15 pF
4 MHz
15 pF
HS
4 MHz
15 pF
8 MHz
15 pF
20 MHz
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
VDD and temperature range for the application.
See the notes following this table for additional
information.
Note 1: Higher capacitance increases the stability
of 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: Rs 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 VDD and temperature range that is
expected for the application.