PIC17C756A MICROCHIP [Microchip Technology], PIC17C756A Datasheet - Page 19

• Manufacturer Part Number: PIC17C756A
• Description: High-Performance 8-bit CMOS EPROM Microcontrollers with 10-bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

4.1.4
In the EC oscillator mode, the OSC1 input can be
driven by CMOS drivers. In this mode, the OSC1/
CLKIN pin is hi-impedance and the OSC2/CLKOUT pin
is the CLKOUT output (4 T
FIGURE 4-4:
4.1.5
Either a prepackaged oscillator can be used, or a sim-
ple oscillator circuit with TTL gates can be built. Pre-
packaged 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 can be used: one with
series resonance, or one with parallel resonance.
Figure 4-5 shows implementation of a parallel resonant
oscillator circuit. The circuit is designed to use the fun-
damental frequency of the crystal. The 74AS04 inverter
performs the 180-degree phase shift that a parallel
oscillator requires. The 4.7 k
negative feedback for stability. The 10 k
ter biases the 74AS04 in the linear region. This could
be used for external oscillator designs.
2000 Microchip Technology Inc.
Clock from
ext. system
CLKOUT
(F
EXTERNAL CLOCK OSCILLATOR
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
OSC
/4)
EXTERNAL CLOCK INPUT
OPERATION (EC OSC
CONFIGURATION)
OSC
OSC2
OSC1
).
resistor provides the
PIC17CXXX
potentiome-
FIGURE 4-5:
Figure 4-6 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
to bias the inverters in their linear region.
FIGURE 4-6:
74AS04
330
10k
+5V
0.1 F
20 pF
XTAL
10 k
resistors provide the negative feedback
74AS04
XTAL
4.7 k
74AS04
330
20 pF
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
PIC17C7XX
10 k
74AS04
74AS04
To Other
Devices
DS30289B-page 19
To Other
Devices
PIC17CXXX
PIC17CXXX
OSC1
OSC1