Table of Contents
Advertisement
8XC196NT USER'S MANUAL
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
) are usually adequate for frequencies above 1 MHz.
L
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
further reduce the effects of noise, use grounded guard rings around the oscillator circuitry and
ground the metallic crystal case.
12-6
To internal
circuitry
Rf
XTAL1
(Input)
Oscillator Enable#
(from powerdown circuitry)
Figure 12-3. On-chip Oscillator Circuit
V CC
XTAL2
(Output)
V SS
A0076-03
. To
SS
Advertisement
Table of Contents
