PIC16F87/88
TABLE 4-1:
Osc Type
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR (FOR
DESIGN GUIDANCE ONLY)
4.0
4.1
OSCILLATOR
CONFIGURATIONS
Typical Capacitor Values
Oscillator Types
Crystal
Freq
Tested:
The PIC16F87/88 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):
C1
C2
LP
XT
32 kHz
200 kHz
1 MHz
4 MHz
4 MHz
8 MHz
20 MHz
33 pF
56 pF
15 pF
15 pF
15 pF
15 pF
15 pF
33 pF
56 pF
15 pF
15 pF
15 pF
15 pF
15 pF
1. LP
2. XT
3. HS
4. RC
Low-Power Crystal
Crystal/Resonator
HS
High-Speed Crystal/Resonator
External Resistor/Capacitor with
FOSC/4 output on RA6
5. RCIO
6. INTIO1
7. INTIO2
8. ECIO
External Resistor/Capacitor with
I/O on RA6
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.
Internal Oscillator with FOSC/4
output on RA6 and I/O on RA7
Internal Oscillator with I/O on RA6
and RA7
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.
External Clock with I/O on RA6
4.2
Crystal Oscillator/Ceramic
Resonators
See the notes following this table for additional
information.
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 PIC16F87/88 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.
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.
FIGURE 4-1:
CRYSTAL OPERATION
(HS, XT, OR LP OSC
CONFIGURATION)
3: Rs may be required in HS mode, as well
as XT mode, to avoid overdriving crystals
with low drive level specification.
OSC1
PIC16F87/88
4: Always verify oscillator performance over
the VDD and temperature range that is
expected for the application.
C1(1)
XTAL
OSC2
(3)
RF
SLEEP
(2)
RS
C2(1)
To Internal
Logic
Note1: 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 MΩ to 10 MΩ).
2003 Microchip Technology Inc.
Preliminary
DS30487B-page 35
MICROCHIP [ MICROCHIP ]
