Kenwood TK-80 Service Manual page 18

SELECTIVE CALL UNIT
DTMF
MIC SW
DTMF
decoder
IC3
Selective
call
decoder
IC1,IC2
5-2. Reset circuit
IC3 monitors Vcc applied to the microcomputer. If the
voltage falls below 2.15V, the IC outputs a reset signal ("L")
to the microcomputer and the CPU initializes all internal data
(including memory channel No. 11 to 80). The reset signal is
not output when the power is turned on or off or 14V is
turned on or off. It is output when the battery voltage level
goes low and 14V is turned on or off.
C34 generates the signal width (td) required to reset the
microcomputer (Fig. 9).
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CIRCUIT DESCRIPTION
LCD ASSY
AT, SCAN
MENU
MODE
DATA
SW
CONTROL UNIT
DATA BUS
Slide Expand I/O
SW IC7
S1,S3
D7~D9
Enable
D12~D15
VCO select
Internal AT control
Outside AT control
uart rx
Reset
reset
IC3
Low voltage
int
detection
D4,D5,Q1,Q2
EEPROM
PC control
Fig. 8 Control block diagram
manuals search engine
Rotary
LCD
encoder
SQL
CLARI
LCD Power
VR Buffer
driver SW
int a/d timer
(int)
CPU
IC5
uart
Buffer Buffer
IC6 IC8 Q3~Q6
Outside
IF-232C
AT
5V
Vcc
4.35V
2.15V
AT UNIT
Internal
AT
POD1,POD2
TX-RX UNIT
timer a/d
(PWM)
a/d SM, VSFM, VSRM
SS, KEY, KYS
int
BOVR
Serial/Parallel
IC4
FINAL UNIT
D1
67
3
1 26
2
IC3
Reset IC
7
td
RESET
Fig. 9 Reset circuit
TK-80
PLL/DDS
IC500~IC502
Serial/Parallel
IC10,IC15,IC16
DAC
IC13
Vcc
IC5
CPU
RESET
RESET
17