Using An External Clock Source - Intel 8XC196MC User Manual

13.5 USING AN EXTERNAL CLOCK SOURCE

To use an external clock source, apply a clock signal to XTAL1 and let XTAL2 float (Figure
13-5). To ensure proper operation, the external clock source must meet the minimum high and
low times (T and T
XHXX
(Figure 13-6). The longer the rise and fall times, the higher the probability that external noise will
affect the clock generator circuitry and cause unreliable operation. See the datasheet for required
XTAL1 voltage drive levels and actual specifications.
External
Clock Input
† Required if TTL driver is used. Not needed if CMOS driver is used.
0.7 V
XTAL1
At power-on, the interaction between the internal amplifier and its feedback capacitance (i.e., the
Miller effect) may cause a load of up to 100 pF at the XTAL1 pin if the signal at XTAL1 is weak
(such as might be the case during start-up of the external oscillator). This situation will go away
when the XTAL1 input signal meets the V
these specifications are met, the XTAL1 pin capacitance will not exceed 20 pF.
) and the maximum rise and fall transition times (T
XLXX
V CC
4.7 kΩ †
Clock Driver
No Connection
Figure 13-5. External Clock Connections
T
XHXX
+ 0.5 V
CC
0.3 V
CC
Figure 13-6. External Clock Drive Waveforms
and V
IL
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MINIMUM HARDWARE CONSIDERATIONS
XTAL1
MCS ® 96
Microcontroller
XTAL2
T
XLXH
0.7 V
CC
T
XLXX
– 0.5 V
0.3 V – 0.5 V
CC
T
XLXL
specifications (listed in the datasheet). If
IH
and T
XLXH XHXL
A0274-03
T
XHXL
+ 0.5 V
A2119-02
13-7
)