Datasheet

PIC16C5X
DS30453E-page 16 Preliminary  1997-2013 Microchip Technology Inc.
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 k resistor
provides the negative feedback for stability. The 10 k
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)
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 k 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)
20 pF
+5V
20 pF
10K
4.7K
10K
74AS04
XTAL
10K
74AS04
PIC16C5X
CLKIN
To Other
Devices
OSC2
Open
330K
74AS04
74AS04
PIC16C5X
CLKIN
To Other
Devices
XTAL
330K
74AS04
0.1 F
OSC2
Open