PIC17C44 Datasheet, PDF (101/241 Pages) Microchip Technology – High-Performance 8-Bit CMOS EPROM/ROM Microcontroller

FIGURE 14-3: CRYSTAL OPERATION,
OVERTONE CRYSTALS (XT
OSC CONFIGURATION)
C1
OSC1
C2
OSC2
SLEEP
0.1 µF
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 14-2: CAPACITOR SELECTION
FOR CERAMIC
RESONATORS
Oscillator
Type
Resonator
Frequency
Capacitor Range
C1 = C2
LF
455 kHz
15 - 68 pF
2.0 MHz
10 - 33 pF
XT
4.0 MHz
22 - 68 pF
8.0 MHz
33 - 100 pF
16.0 MHz
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.
PIC17C4X
TABLE 14-3: CAPACITOR SELECTION
FOR CRYSTAL OSCILLATOR
Osc
Type
Freq
C1
C2
LF
32 kHz⁽¹⁾ 100-150 pF 100-150 pF
1 MHz 10-33 pF
10-33 pF
2 MHz 10-33 pF
10-33 pF
XT
2 MHz 47-100 pF
4 MHz
8 MHz ⁽²⁾
15-68 pF
15-47 pF
16 MHz
TBD
25 MHz 15-47 pF
32 MHz ⁽³⁾
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. RS 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 VDD > 4.5V, C1 = C2 ≈ 30 pF is recom-
mended.
2: RS of 330Ω 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
1.0 MHz
2.0 MHz
4.0 MHz
8.0 MHz
16.0 MHz
25 MHz
32 MHz
Epson C-001R32.768K-A
ECS-10-13-1
ECS-20-20-1
ECS-40-20-1
ECS ECS-80-S-4
ECS-80-18-1
ECS-160-20-1
CTS CTS25M
CRYSTEK HF-2
± 20 PPM
± 50 PPM
± 50 PPM
± 50 PPM
± 50 PPM
TBD
± 50 PPM
± 50 PPM
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 TOSC).
FIGURE 14-4: EXTERNAL CLOCK INPUT
OPERATION (EC OSC
CONFIGURATION)
Clock from
ext. system
CLKOUT
(FOSC/4)
OSC1
PIC17CXX
OSC2
© 1996 Microchip Technology Inc.
DS30412C-page 101