PIC16F8X_13 Datasheet, PDF (40/128 Pages) Microchip Technology – 18-pin Flash/EEPROM 8-Bit Microcontrollers

PIC16F8X
FIGURE 8-4:
EXTERNAL CLOCK INPUT
OPERATION (HS, XT OR LP
OSC CONFIGURATION)
Clock from
ext. system
Open
OSC1
PIC16FXX
OSC2
TABLE 8-1
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
Ranges Tested:
Mode
Freq
OSC1/C1 OSC2/C2
XT
455 kHz 47 - 100 pF 47 - 100 pF
2.0 MHz 15 - 33 pF 15 - 33 pF
4.0 MHz 15 - 33 pF 15 - 33 pF
HS
8.0 MHz 15 - 33 pF 15 - 33 pF
10.0 MHz 15 - 33 pF 15 - 33 pF
Note : Recommended values of C1 and C2 are identical to
the ranges tested table.
Higher capacitance increases the stability of the
oscillator but also increases the start-up time.
These values are for design guidance only. Since
each resonator has its own characteristics, the user
should consult the resonator manufacturer for the
appropriate values of external components.
Resonators Tested:
455 kHz Panasonic EFO-A455K04B 0.3%
2.0 MHz Murata Erie CSA2.00MG 0.5%
4.0 MHz Murata Erie CSA4.00MG 0.5%
8.0 MHz Murata Erie CSA8.00MT  0.5%
10.0 MHz Murata Erie CSA10.00MTZ 0.5%
None of the resonators had built-in capacitors.
TABLE 8-2
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
Mode
Freq
OSC1/C1 OSC2/C2
LP
32 kHz 68 - 100 pF 68 - 100 pF
200 kHz 15 - 33 pF 15 - 33 pF
XT
100 kHz 100 - 150 pF 100 - 150 pF
2 MHz
15 - 33 pF 15 - 33 pF
4 MHz
15 - 33 pF 15 - 33 pF
HS
4 MHz
15 - 33 pF 15 - 33 pF
10 MHz 15 - 33 pF 15 - 33 pF
Note :
Higher capacitance increases the stability of
oscillator but also increases the start-up time.
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 speci-
fication. Since each crystal has its own characteris-
tics, the user should consult the crystal
manufacturer for appropriate values of external
components.
For VDD > 4.5V, C1 = C2  30 pF is recommended.
DS30430D-page 40
Crystals Tested:
32.768 kHz
100 kHz
200 kHz
1.0 MHz
2.0 MHz
4.0 MHz
10.0 MHz
Epson C-001R32.768K-A  20 PPM
Epson C-2 100.00 KC-P  20 PPM
STD XTL 200.000 KHz  20 PPM
ECS ECS-10-13-2
 50 PPM
ECS ECS-20-S-2
 50 PPM
ECS ECS-40-S-4
 50 PPM
ECS ECS-100-S-4
 50 PPM
8.2.3 EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
Either a prepackaged oscillator can be used or a simple
oscillator circuit with TTL gates can be built.
Prepackaged oscillators provide a wide operating
range and better stability. A well-designed crystal
oscillator will provide good performance with TTL
gates. Two types of crystal oscillator circuits are
available; one with series resonance, and one with
parallel resonance.
Figure 8-5 shows a parallel resonant oscillator circuit.
The circuit is designed to use the fundamental
frequency of the crystal. The 74AS04 inverter performs
the 180-degree phase shift that a parallel oscillator
requires. The 4.7 k resistor provides negative
feedback for stability. The 10 k potentiometer biases
the 74AS04 in the linear region. This could be used for
external oscillator designs.
FIGURE 8-5:
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
+5V
10k
4.7k
74AS04
To Other
Devices
74AS04
PIC16FXX
CLKIN
10k
XTAL
10k
20 pF 20 pF
Figure 8-6 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental
frequency of the crystal. The inverter performs a
180-degree phase shift. The 330 k resistors provide
the negative feedback to bias the inverters in their
linear region.
 1996-2013 Microchip Technology Inc.