Kenwood TH-77A Service Manual page 13

TH-77A/E
CIRCUIT DESCRIPTION
(7) Microcomputer and Peripheral Circuits
7-1 Reset and Backup Circuits changes the output signal from high to low. The microcomput-
Alow pulse of approximately 1 ms duration is output from reset er enters the backup mode when microcomputer port INT4 is
circuits C76 and Q19 when the B power is turned on. Micro- made low. Microcomputer [C12 is reset by microcomputer
computer |C10 is then reset. When the B power is turned off, IC10.
voltage detector circuit C9 detects the 5-V line drop and
Power SW Power SW
ON OFF
SV
B
0
!
0
t
INT 4] 5VF fees Voltage
fo)
Timing chart
Ic9
VOLTAGE DETECTOR
Fig. 10 Reset and backup circuit
13