Hitachi RAC-25FX8, Service Manual

Page: 74 / 191

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2. Reset Circuit
Timing chart
C521
R521
C522
C524
5
3
IC521
1
2
5V
R522
R523
7
0V
5 ． 0V
4
．
4V
5 ． 0V
4
．
2V
② pin of IC521 supply voltage
RES canceling voltage
RES detecting voltage
① pin of IC521 output voltage
or
⑦
pin of microcomputer
Reset circuit is to initialize the indoor unit microcomputer when switching ON the power or after recovering from power
failure.
Microcomputer operates when ⑦ pin of the indoor unit microcomputer (reset input) is "Lo" for resetting and "Hi" for hitting.
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,
① pin of IC521 supply voltage and ⑦ pin of microcomputer becomes Hi when DC5V line
rises and reaches approximately 4.4V or higher.
Then, resetting will be cancelled and microcomputer starts operating.
After shutting down the power,
① pin of IC521 supply voltage and ⑦ pin of microcomputer becomes Lo when DC5V line
falls and reaches approximately 4.2V or lower.
Then, the microcomputer will be in reset condition.
Fig.2-1
Fig.2-2
Reset
Microcomputer
Voltage
Voltage