Intel 80C196NU ユーザーズマニュアル

11-6

Figure 11-4 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

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

SS

. To

further reduce the effects of noise, use grounded guard rings around the oscillator circuitry and
ground the metallic crystal case.

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.

8XC196

Device

XTAL2

XTAL1

Quartz Crystal

C1

C2

A0273-02

Note:
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.