Description Of Main Circuit Operation - Hitachi RAI-25NH5 Service Manual

DESCRIPTION OF MAIN CIRCUIT OPERATION

MODEL RAI-25NH5, RAI-35NH5
1. Reset Circuit
Voltage supply to
pin 2 of IC521
Voltage at pin
of microcomputer
The reset circuit initializes the microcomputer program when power is ON or OFF.
G
Low voltage at pin
G
When power "ON" 5V voltage rises and reaches 4.4V, pin 1 of IC521 is set to "Hi". At this time the
G
microcomputer starts operation.
When power "OFF" voltage drops and reaches 4.2V, pin 1 of IC521 is set to "Low". This will RESET the
G
microcomputer.
5V
2
1
5
3
IC521
Voltage
5.0V
Reset release at 4.4V
voltage
5.0V
7
resets the microcomputer and Hi activates the microcomputer.
7
R522
0V
Fig. 1-1
Fig. 1-2
– 56 –
NORMAL : HI
RESET : LO
7
RES
Microcomputer
Reset enter at 4.2V