Datasheet

 1996 Microchip Technology Inc. DS30412C-page 101
PIC17C4X
FIGURE 14-3: CRYSTAL OPERATION,
OVERTONE CRYSTALS (XT
OSC CONFIGURATION)
TABLE 14-2: CAPACITOR SELECTION
FOR CERAMIC
RESONATORS
Oscillator
Type
Resonator
Frequency
Capacitor Range
C1 = C2
LF 455 kHz
2.0 MHz
15 - 68 pF
10 - 33 pF
XT 4.0 MHz
8.0 MHz
16.0 MHz
22 - 68 pF
33 - 100 pF
33 - 100 pF
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 ± 0.3%
2.0 MHz Murata Erie CSA2.00MG ± 0.5%
4.0 MHz Murata Erie CSA4.00MG ± 0.5%
8.0 MHz Murata Erie CSA8.00MT ± 0.5%
16.0 MHz Murata Erie CSA16.00MX ± 0.5%
Resonators used did not have built-in capacitors.
C1
C2
0.1 µF
SLEEP
OSC2
OSC1
PIC17C42
To filter the fundamental frequency
1
LC2
=
(2πf)
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
Freq C1 C2
LF 32 kHz
(1)
1 MHz
2 MHz
100-150 pF
10-33 pF
10-33 pF
100-150 pF
10-33 pF
10-33 pF
XT 2 MHz
4 MHz
8 MHz
(2)
16 MHz
25 MHz
32 MHz
(3)
47-100 pF
15-68 pF
15-47 pF
TBD
15-47 pF
0
(3)
47-100 pF
15-68 pF
15-47 pF
TBD
15-47 pF
0
(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 ≈ 30 pF is recom-
mended.
2: R
S
of 330 Ω 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 ± 20 PPM
1.0 MHz ECS-10-13-1 ± 50 PPM
2.0 MHz ECS-20-20-1 ± 50 PPM
4.0 MHz ECS-40-20-1 ± 50 PPM
8.0 MHz ECS ECS-80-S-4
ECS-80-18-1
± 50 PPM
16.0 MHz ECS-160-20-1 TBD
25 MHz CTS CTS25M ± 50 PPM
32 MHz CRYSTEK HF-2 ± 50 PPM
Clock from
ext. system
OSC1
OSC2
PIC17CXX
CLKOUT
(F
OSC/4)