Intel 8XC196NT, User Manual

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8XC196NT USER’S MANUAL
12-6
Figure 12-3. On-chip Oscillator Circuit
Figure 12-4 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.
Rf
XTAL2
(Output)
VCC
XTAL1
(Input)
Oscillator Enable#
(from powerdown circuitry)
To internal
circuitry
A0076-03
VSS