– 39 –
● The reset circuit is used to reset the program to its initial settings when the power is turned on or when the power is
recovered after a power failure.
● The micro computer is reset when the reset input is “Hi”, and reset operation is possible when the reset input is “Lo”.
● The waveforms at each point when the power is turned on and off are shown in the Fig. 2-2.
● When the power is turned on, the voltages of the DC 12V line and DC 5V line are increased. When the voltage of DC
12V line reaches about 7V, ZD701 is turned ON, the potential of Q701’s base rises and Q701 is turned ON. At this time
the collector of Q701 is set to “LO” and cause Q702 to conduct. The collector of Q702 is set to “HI” and the reset input
of the micro computer is set to “HI” also. The DC 5V voltage has already become 5V at this time and the micro computer
starts operate.
● When the power is turned OFF, the voltage of the DC 12V line decreases. When it drops about 7V, ZD701 is turned OFF,
and this will turn Q701 and Q702 OFF rapidly. The reset input of the micro computer is set to “LO” and the micro computer
is set to reset mode.
Service Switch
2. Service Switch Circuit
21
NORMAL
COOL
COOL
R315
0V
5V
MICON
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