PIC12F519 Microchip Technology, PIC12F519 Datasheet - Page 40

• Manufacturer Part Number: PIC12F519
• Description: 8-Bit Flash Microcontroller
• Manufacturer: Microchip Technology

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PIC12F519
8.2.3
Either a prepackaged oscillator or a simple oscillator
circuit with TTL gates can be used as an external crystal
oscillator circuit. 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 can be
used: one with parallel resonance, or one with series
resonance.
Figure 8-3 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 kΩ resistor provides the
negative feedback for stability. The 10 kΩ potentiome-
ters bias the 74AS04 in the linear region. This circuit
could be used for external oscillator designs.
FIGURE 8-3:
Figure 8-4 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 in a series resonant oscillator
circuit. The 330 Ω resistors provide the negative
feedback to bias the inverters in their linear region.
FIGURE 8-4:
DS41319A-page 38
74AS04
330
10k
+5V
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
20 pF
0.1 mF
10k
XTAL
74AS04
XTAL
4.7k
74AS04
330
20 pF
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
10k
74AS04
74AS04
To Other
Devices
To Other
Devices
PIC12F519
CLKIN
PIC12F519
CLKIN
Preliminary
8.2.4
For timing insensitive applications, the RC circuit option
offers additional cost savings. The RC oscillator fre-
quency is a function of the supply voltage, the resistor
(R
temperature. In addition to this, the oscillator frequency
will vary from unit-to-unit due to normal process param-
eter variation. Furthermore, the difference in lead frame
capacitance between package types will also affect the
oscillation frequency, especially for low C
The user also needs to take into account variation due
to tolerance of external R and C components used.
Figure 8-5 shows how the R/C combination is con-
nected to the PIC12F519 device. For R
below 3.0 kΩ, the oscillator operation may become
unstable, or stop completely. For very high R
(e.g., 1 MΩ), the oscillator becomes sensitive to noise,
humidity and leakage. It is recommended keeping
R
Although the oscillator will operate with no external
capacitor (C
values above 20 pF for noise and stability reasons.
With no or small external capacitance, the oscillation
frequency can vary dramatically due to changes in
external capacitances, such as PCB trace capacitance
or package lead frame capacitance.
Section 11.0 “Electrical Characteristics”, shows RC
frequency variation from part-to-part due to normal
process variation. The variation is larger for larger val-
ues of R (since leakage current variation will affect RC
frequency more for large R) and for smaller values of C
(since variation of input capacitance will affect RC
frequency more).
Also, see the Electrical Specifications section for
variation of oscillator frequency due to V
R
to operating temperature for given R, C and V
values.
FIGURE 8-5:
EXT
EXT
C
V
EXT
R
SS
EXT
EXT
/C
between 5.0 kΩ and 100 kΩ.
) and capacitor (C
V
EXT
DD
EXTERNAL RC OSCILLATOR
values, as well as frequency variation due
EXT
= 0 pF), it is recommended using
EXTERNAL RC
OSCILLATOR MODE
© 2007 Microchip Technology Inc.
EXT
OSC1
N
) values, and the operating
PIC16F519
DD
EXT
EXT
EXT
Internal
clock
for given
values.
values
values
DD