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1996 Microchip Technology Inc.
DS30412B-page 101
PIC17C4X
FIGURE 14-3: CRYSTAL OPERATION,
OVERTONE CRYSTALS (XT
OSC CONFIGURATION)
TABLE 14-2:
CAPACITOR SELECTION
FOR CERAMIC
RESONATORS
Oscillator
Type
LF
Resonator
Frequency
455 kHz
2.0 MHz
4.0 MHz
8.0 MHz
16.0 MHz
Capacitor Range
C1 = C2
15 - 68 pF
10 - 33 pF
22 - 68 pF
33 - 100 pF
33 - 100 pF
XT
Higher capacitance increases the stability of the
oscillator but also increases the start-up time. These
values are for design guidance only. Since each reso-
nator has its own characteristics, the user should
consult the resonator manufacturer for appropriate
values of external components.
Resonators Used:
455 kHz
Panasonic EFO-A455K04B
2.0 MHz
Murata Erie CSA2.00MG
4.0 MHz
Murata Erie CSA4.00MG
8.0 MHz
Murata Erie CSA8.00MT
16.0 MHz
Murata Erie CSA16.00MX
Resonators used did not have built-in capacitors.
±
±
±
±
±
0.3%
0.5%
0.5%
0.5%
0.5%
C1
C2
0.1
μ
F
SLEEP
OSC2
OSC1
PIC17C42
To filter the fundamental frequency
L1
π
f)
2
Where f = tank circuit resonant frequency. This should be
midway between the fundamental and the 3rd overtone
frequencies of the crystal.
TABLE 14-3:
CAPACITOR SELECTION
FOR CRYSTAL
OSCILLATOR
14.2.3
EXTERNAL CLOCK OSCILLATOR
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/CLK-
OUT pin is the CLKOUT output (4 T
OSC
).
FIGURE 14-4: EXTERNAL CLOCK INPUT
OPERATION (EC OSC
CONFIGURATION)
Osc
Type
LF
Freq
C1
C2
32 kHz
1 MHz
2 MHz
2 MHz
4 MHz
8 MHz
16 MHz
25 MHz
32 MHz
(1)
100-150 pF
10-33 pF
10-33 pF
47-100 pF
15-68 pF
15-47 pF
TBD
15-47 pF
0
100-150 pF
10-33 pF
10-33 pF
47-100 pF
15-68 pF
15-47 pF
TBD
15-47 pF
0
XT
(2)
(3)
(3)
(3)
Higher capacitance increases the stability of the
oscillator but also increases the start-up time and the
oscillator current. These values are for design guid-
ance only. R
S
may be required in XT mode to avoid
overdriving the crystals with low drive level specifica-
tion. Since each crystal has its own characteristics,
the user should consult the crystal manufacturer for
appropriate values for external components.
Note 1: For V
DD
> 4.5V, C1 = C2
mended.
2: R
S
of 330
is required for a capacitor com-
bination of 15/15 pF.
3:
Only the capacitance of the board was present.
Crystals Used:
32.768 kHz
Epson C-001R32.768K-A
1.0 MHz
ECS ECS-10-13-2
2.0 MHz
ECS ECS-20-S-1
4.0 MHz
ECS ECS-40-S-4
8.0 MHz
ECS ECS-80-S-4
16.0 MHz
TBD
25 MHz
CTS CTS25M
32 MHz
CRYSTEK HF-2
≈
30 pF is recom-
±
±
±
±
±
TBD
±
50 PPM
±
50 PPM
20 PPM
50 PPM
50 PPM
50 PPM
50 PPM
Clock from
ext. system
OSC1
OSC2
PIC17CXX
CLKOUT
(F
OSC
/4)