參數(shù)資料
型號(hào)： 16F628
廠商： Microchip Technology Inc.
英文描述： CAT 5E CROSSOVER PATCH CORD CABLE BLUE 1 FT
中文描述： 基于閃存的8位CMOS微控制器
文件頁數(shù)： 97/168頁
文件大?。?/td> 3760K
代理商： 16F628
2002 Microchip Technology Inc.
Preliminary
DS40044A-page 95
PIC16F627A/628A/648A
14.2
Oscillator Configurations
14.2.1
OSCILLATOR TYPES
The PIC16F627A/628A/648A can be operated in eight
different oscillator options. The user can program three
configuration bits (FOSC2 through FOSC0) to select
one of these eight modes:
LP
Low Power Crystal
XT
Crystal/Resonator
HS
High Speed Crystal/Resonator
RC
External Resistor/Capacitor (2 modes)
INTOSC Internal Precision Oscillator (2 modes)
EC
External Clock In
14.2.2
CRYSTAL OSCILLATOR / CERAMIC
RESONATORS
In XT, LP or HS modes a crystal or ceramic resonator
is connected to the OSC1 and OSC2 pins to establish
oscillation (Figure 14-1). The PIC16F627A/628A/648A
oscillator design requires the use of a parallel cut crys-
tal. Use of a series cut crystal may give a frequency out
of the crystal manufacturers specifications. When in
XT, LP or HS modes, the device can have an external
clock source to drive the OSC1 pin (Figure 14-4).
FIGURE 14-1:
CRYSTAL OPERATION
(OR CERAMIC
RESONATOR) (HS, XT OR
LP OSC
CONFIGURATION)
TABLE 14-1:
CAPACITOR SELECTION FOR
CERAMIC RESONATORS
TABLE 14-2:
CAPACITOR SELECTION FOR
CRYSTAL OSCILLATOR
14.2.3
EXTERNAL CRYSTAL OSCILLATOR
CIRCUIT
Either a prepackaged oscillator can be used or a simple
oscillator circuit with TTL gates can be built.
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 series resonance, or one with parallel
resonance.
Figure 14-2 shows implementation of a parallel reso-
nant oscillator circuit. The circuit is designed to use the
fundamental frequency of the crystal. The 74AS04
inverter performs the 180
°
phase shift that a parallel
oscillator requires. The 4.7 k
resistor provides the
negative
feedback
for
potentiometers bias the 74AS04 in the linear region.
This could be used for external oscillator designs.
stability.
The
10 k
Note
1:
A series resistor may be required for AT strip cut
crystals.
See Table 14-1 and Table 14-2 for recommended
values of C1 and C2.
2:
C1
C2
XTAL
OSC2
RS
(1)
OSC1
RF
SLEEP
PIC16F627A/628A/648A
F
OSC
Mode
Freq
OSC1(C1)
OSC2(C2)
XT
455 kHz
2.0 MHz
4.0 MHz
22 - 100 pF
15 - 68 pF
15 - 68 pF
22 - 100 pF
15 - 68 pF
15 - 68 pF
HS
8.0 MHz
16.0 MHz
10 - 68 pF
10 - 22 pF
10 - 68 pF
10 - 22 pF
Note:
Higher capacitance increases the stability of the oscil-
lator but also increases the start-up time. These values
are for design guidance only. Since each resonator has
its own characteristics, the user should consult the res-
onator manufacturer for appropriate values of external
components.
Mode
Freq
OSC1(C1)
OSC2(C2)
LP
32 kHz
200 kHz
15 - 30 pF
0 - 15 pF
15 - 30 pF
0 - 15 pF
XT
100 kHz
2 MHz
4 MHz
68 - 150 pF
15 - 30 pF
15 - 30 pF
150 - 200 pF
15 - 30 pF
15 - 30 pF
HS
8 MHz
10 MHz
20 MHz
15 - 30 pF
15 - 30 pF
15 - 30 pF
15 - 30 pF
15 - 30 pF
15 - 30 pF
Note:
Higher capacitance increases the stability of the oscil-
lator but also increases the start-up time. These values
are for design guidance only. A series resistor (RS)
may be required in HS mode as well as XT mode to
avoid overdriving crystals with low drive level specifica-
tion. Since each crystal has its own characteristics, the
user should consult the crystal manufacturer for appro-
priate values of external components.
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