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ZN448/9
7
Fig.8 Clock circuit external components
BUSY
OUTPUT
The
BUSY
output, shown in Fig.7, utilises a passive pull-up for
CMOS/TTL compatibility. This allows up to four
BUSY
outputs
to be wire-ANDed together to form a common interrupt line.
Fig.7
BUSY
output
ON-CHIP CLOCK
The on-chip clock operates with only a single external
capacitor connected between pin 3 and ground, as shown in
Fig.8a. A graph of typical oscillator frequency versus
capacitance is given in Fig.9. The oscillator frequency may be
trimmed by means of an external resistor in series with the
capacitor, as shown in Fig.8b. However, due to processing
tolerance, the absolute clock frequency may vary
considerably between devices. For optimum accuracy and
stability of the oscillator frequency, it may be possible to use
a crystal or ceramic resonator with suitable load components,
as shown in Fig.8c. The final option is to overdrive the
oscillator input with an external clock signal from a TTL or
CMOS gate, as shown in Fig.8d.
9
3OSC
GND
9
3
3
2k
MAX
1.2k
VCC
9
3
Xtal
1MHz
,
56pF
2200pF
,
4.7k
,
Load circuit to suit
device used
c) Crystal or resonator
,
a) Fixed/variable capacitor
b) Fixed capacitor + variable resistor
d) External TTL or CMOS drive