Hitachi RAS-25WX8 Manuel De Maintenance page 72

2. Reset Circuit
Timing chart
or
Reset circuit is to initialize the indoor unit microcomputer when switching ON the power or after recovering from power
failure.
Microcomputer operates when
Waveform of each part when switching ON the power and when shutting down is shown in the Fig. 2-2.
After switching ON the power,
rises and reaches approximately 4.4V or higher.
Then, resetting will be cancelled and microcomputer starts operating.
After shutting down the power,
falls and reaches approximately 4.2V or lower.
Then, the microcomputer will be in reset condition.
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5
Voltage
pin of IC521 supply voltage
RES canceling voltage
4 4V
Voltage
pin of IC521 output voltage
pin of microcomputer
pin of the indoor unit microcomputer (reset input) is "Lo" for resetting and "Hi" for heating.
pin of IC521 supply voltage and
pin of IC521 supply voltage and
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5V
2
R522
1
3
IC521
0V
Fig.2-1
5 0V
5 0V
Fig.2-2
pin of microcomputer becomes Hi when DC5V line
pin of microcomputer becomes Lo when DC5V line
– 71 –
Reset
7
Microcomputer
RES detecting voltage
4 2V