12F508 Microchip Technology, 12F508 Datasheet - Page 44

• Manufacturer Part Number: 12F508
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• Manufacturer: Microchip Technology

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PIC12F508/509/16F505
TABLE 7-2:
7.2.3
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 perfor-
mance with TTL gates. Two types of crystal oscillator
circuits can be used: one with parallel resonance, or
one with series resonance.
Figure 7-3 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 k
negative feedback for stability. The 10 k
ters bias the 74AS04 in the linear region. This circuit
could be used for external oscillator designs.
DS41236B-page 42
Note 1:
HS
Type
Osc
LP
XT
(3)
2:
3:
Resonator
For V
recommended.
These values are for design guidance
only. Rs may be required to avoid over-
driving crystals with low drive level specifi-
cation. Since each crystal has its own
characteristics, the user should consult
the crystal manufacturer for appropriate
values of external components.
PIC16F505 only.
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
32 kHz
200 kHz
20 MHz
1 MHz
4 MHz
Freq.
DD
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR –
PIC12F508/509/16F505
(1)
> 4.5V, C1 = C2
Cap. Range
47-68 pF
15-47 pF
15 pF
15 pF
15 pF
C1
resistor provides the
30 pF is
Cap. Range
47-68 pF
15-47 pF
potentiome-
15 pF
15 pF
15 pF
(2)
C2
Preliminary
FIGURE 7-3:
Figure 7-4 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
feedback to bias the inverters in their linear region.
FIGURE 7-4:
7.2.4
For timing insensitive applications, the RC device
option offers additional cost savings. The RC oscillator
frequency is a function of the supply voltage, the resis-
tor (R
ing temperature. In addition to this, the oscillator
frequency will vary from unit-to-unit due to normal pro-
cess parameter variation. Furthermore, the difference
in lead frame capacitance between package types will
also affect the oscillation frequency, especially for low
C
variation due to tolerance of external R and C
components used.
Figure 7-5 shows how the R/C combination is con-
nected to the PIC12F508/509/16F505 devices. For
R
become unstable, or stop completely. For very high
R
sensitive to noise, humidity and leakage. Thus, we
recommend keeping R
100 k .
EXT
EXT
EXT
74AS04
330
EXT
values. The user also needs to take into account
values below 3.0 k , the oscillator operation may
values (e.g., 1 M ), the oscillator becomes
10k
) and capacitor (C
+5V
EXTERNAL RC OSCILLATOR
20 pF
0.1 mF
10k
XTAL
74AS04
XTAL
4.7k
74AS04
330
resistors provide the negative
20 pF
EXTERNAL PARALLEL
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
EXTERNAL SERIES
RESONANT CRYSTAL
OSCILLATOR CIRCUIT
© 2005 Microchip Technology Inc.
EXT
EXT
10k
74AS04
) values, and the operat-
between 5.0 k
74AS04
To Other
Devices
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Devices
PIC16F505
PIC12F508
PIC12F509
CLKIN
PIC16F505
PIC12F508
PIC12F509
CLKIN
and