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11. Reset circuit
8J-HIC
Micro
computer
(AX-8J00)
~
To trip signal
synthesis circuit
Fig. 11-1
Reset circuit performs initial setting of the microcomputer program before power is turned on.
Microcomputer resets program with reset voltage set to Lo, and program can be operated with Hi.
Fig. 11-1 shows the reset circuit and Fig. 11-2 shows waveform at each point when power is turned on and off.
When power is turned on; 12V line and 5V line voltages rise and 12V line voltage reaches 7.2V (Zenor voltage of
ZD501), D501 is turned ON, Q301 and Q302 are turned ON and reset voltage input to pin @ of microcomputer is set
to Hi. By ZD501, reset voltage maintains input of pin @ at Lo until Voo of microcomputer rises to 5V to obtain operable
status.
@
When power is shut off and potential of 12V is lowered, ZD501 is shifted to OFF. However, since reset voltage is
feed back to Q301 by R312, maintains ON state until 12V line voltage drops to about 7.6V. This prevents reset voltage
from chattering due to voltage change in 12V line.
12V line
Za
oF
2o
S s
V fi
25
5V
line
&>
Reset voltage
Time
12V line
wu
12
oe
2
sf
= s 6
5V line
©
Reset
voltage
Time
Fig. 11-2
—154—
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