Hitachi RAS-18YH4 Service Manual page 58

6-2. Reset Circuit
MAIN P.W.B.
12V
0V 0V 0V 0V
The reset circuit initializes the microcomputer program when Power is "ON" from "OFF".
Low voltage at pin 48 resets the microcomputer , and HI activates the microcomputer.
Fig. 6-7 shows the reset circuit and Fig. 6-8 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 10.9V an
reset voltage input to pin 48 of microcomputer is set to Hi .
Reset voltage will be hold "Hi" until the 12V line voltage drops to 9.90V even though the power shuts
down.
12
6
0
12
6
0
5V
D208
R287
8
2
−
+
3
IC5(1/2)
R288
10.9V
12V line
5V line
Reset volage
0V
1
R252
C204
0V
Fig. 6-7
12V line
5V line
Reset volage
9.9V
Fig. 6-8
– 61 –
Microcomputer
56
RESET OUT.
48
RESET
Time
Time