Intel 8XC196MD 用户手册
8XC196MC, MD, MH USER’S MANUAL
13-6
Figure 13-4 shows the connections between the external crystal and the device. When designing
an external oscillator circuit, consider the effects of parasitic board capacitance, extended oper-
ating temperatures, and crystal specifications. Consult the manufacturer’s datasheet for perfor-
mance specifications and required capacitor values. With high-quality components, 20 pF load
capacitors (C
an external oscillator circuit, consider the effects of parasitic board capacitance, extended oper-
ating temperatures, and crystal specifications. Consult the manufacturer’s datasheet for perfor-
mance specifications and required capacitor values. With high-quality components, 20 pF load
capacitors (C
L
) are usually adequate for frequencies above 1 MHz.
Noise spikes on the XTAL1 or XTAL2 pin can cause a miscount in the internal clock-generating
circuitry. Capacitive coupling between the crystal oscillator and traces carrying fast-rising digital
signals can introduce noise spikes. To reduce this coupling, mount the crystal oscillator and ca-
pacitors near the device and use short, direct traces to connect to XTAL1, XTAL2, and V
circuitry. Capacitive coupling between the crystal oscillator and traces carrying fast-rising digital
signals can introduce noise spikes. To reduce this coupling, mount the crystal oscillator and ca-
pacitors near the device and use short, direct traces to connect to XTAL1, XTAL2, and V
SS
. To
further reduce the effects of noise, use grounded guard rings around the oscillator circuitry and
ground the metallic crystal case.
ground the metallic crystal case.
Figure 13-4. External Crystal Connections
In cost-sensitive applications, you may choose to use a ceramic resonator instead of a crystal os-
cillator. Ceramic resonators may require slightly different load capacitor values and circuit con-
figurations. Consult the manufacturer’s datasheet for the requirements.
cillator. Ceramic resonators may require slightly different load capacitor values and circuit con-
figurations. Consult the manufacturer’s datasheet for the requirements.
XTAL2
XTAL1
Quartz Crystal
C1
C2
A0273-03
Note:
Mount the crystal and capacitors close to the device using
short, direct traces to XTAL1, XTAL2, and Vss. When
Mount the crystal and capacitors close to the device using
short, direct traces to XTAL1, XTAL2, and Vss. When
using a crystal, C1=C2
≈
20 pF. When using a ceramic
resonator, consult the manufacturer for recommended
oscillator circuitry.
oscillator circuitry.
MCS® 96
Microcontroller