Hitachi RAS-E14H2A - Description of Main Circuit Operation

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2
1
7
3
5
NORMAL : HI
RESET : LO
RES
Microcomputer
C524
C522
C521
R551
IC521
0V
R552
5V
Power "OFF"
Power "ON"
Reset enter at 4.2V
Reset release at 4.4V
Voltage
Voltage
Voltage supply to
pin 2 of IC521
Voltage at pin 7
of microcomputer
5.0V
Fig. 1-2
Fig. 1-1
5.0V
DESCRIPTION OF MAIN CIRCUIT OPERATION
MODEL RAS-E14H2A
1. Reset Circuit
The reset circuit initializes the microcomputer program when power is ON or OFF.
Low voltage at pin 7 resets the microcomputer and Hi activates the microcomputer.
When power “ON” 5V voltage rises and reaches 4.4V, pin 1 of IC521 is set to “Hi”. At this time the microcomputer
starts operation.
When power “OFF” voltage drops and reaches 4.2V, pin 1 of IC521 is set to “Low”. This will RESET the
microcomputer.