PIC16C58B-40 Datasheet, PDF (18/194 Pages) Microchip Technology – EPROM/ROM-Based 8-bit CMOS Microcontroller Series

PIC16C5X
4.3 External Crystal Oscillator Circuit
Either a prepackaged oscillator or a simple oscillator
circuit with TTL gates can be used as an external crys-
tal oscillator circuit. Prepackaged oscillators provide a
wide operating range and better stability. A well-
designed crystal oscillator will provide good perfor-
mance with TTL gates. Two types of crystal oscillator
circuits can be used: one with parallel resonance, or
one with series resonance.
Figure 4-3 shows an implementation example of a par-
allel 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 kΩ resistor
provides the negative feedback for stability. The 10 kΩ
potentiometers bias the 74AS04 in the linear region.
This circuit could be used for external oscillator
designs.
FIGURE 4-3:
EXAMPLE OF EXTERNAL
PARALLEL RESONANT
CRYSTAL OSCILLATOR
CIRCUIT (USING XT, HS
OR LP OSCILLATOR
MODE)
+5V
10K
4.7K
74AS04
To Other
Devices
74AS04
PIC16C5X
CLKIN
XTAL
Open
10K
OSC2
10K
20 pF 20 pF
Figure 4-4 shows a series resonant oscillator circuit.
This circuit is also designed to use the fundamental fre-
quency of the crystal. The inverter performs a 180-
degree phase shift in a series resonant oscillator cir-
cuit. The 330 kΩ resistors provide the negative feed-
back to bias the inverters in their linear region.
FIGURE 4-4:
EXAMPLE OF EXTERNAL
SERIES RESONANT
CRYSTAL OSCILLATOR
CIRCUIT (USING XT, HS
OR LP OSCILLATOR
MODE)
330K
74AS04
330K
74AS04
0.1 µF
XTAL
To Other
Devices
74AS04
PIC16C5X
CLKIN
Open
OSC2
DS30453D-page 16
Preliminary
© 2002 Microchip Technology Inc.