PIC16C56A Microchip Technology Inc., PIC16C56A Datasheet - Page 18

• Manufacturer Part Number: PIC16C56A
• Description: Eprom/rom-based 8-bit Cmos Microcontroller Series
• Manufacturer: Microchip Technology Inc.

PIC16C5X
4.3
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
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:
DS30453D-page 16
10K
External Crystal Oscillator Circuit
+5V
20 pF
10K
74AS04
XTAL
4.7K
20 pF
EXAMPLE OF EXTERNAL
PARALLEL RESONANT
CRYSTAL OSCILLATOR
CIRCUIT (USING XT, HS
OR LP OSCILLATOR
MODE)
10K
74AS04
Open
To Other
Devices
PIC16C5X
CLKIN
OSC2
resistor
Preliminary
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
back to bias the inverters in their linear region.
FIGURE 4-4:
74AS04
330K
0.1 F
XTAL
resistors provide the negative feed-
74AS04
330K
EXAMPLE OF EXTERNAL
SERIES RESONANT
CRYSTAL OSCILLATOR
CIRCUIT (USING XT, HS
OR LP OSCILLATOR
MODE)
2002 Microchip Technology Inc.
74AS04
Open
To Other
Devices
PIC16C5X
CLKIN
OSC2