Kenwood TK-80, Service Manual

Page: 18 / 125

TK-80
17
LCD
driver
EEPROM
IC6
Buffer
IC8
Buffer
Q3~Q6
IF-232C
Outside
AT
DTMF
MIC SW
DTMF
decoder
IC3
Selective
call
decoder
IC1,IC2
LCD
Power
SW
VR Buffer
Rotary
encoder
SW
AT, SCAN
MENU
MODE
DATA
SQL
CLARI
Expand I/O
IC7
Slide
SW
Reset
IC3
Low voltage
detection
D4,D5,Q1,Q2
S1,S3
D7~D9
D12~D15
DATA BUS
Enable
VCO select
Internal AT control
Outside AT control
uart rx
reset
int
int a/d a/d timer
(int)
timer
(PWM)
Internal
AT
AT UNIT
LCD ASSY SELECTIVE CALL UNIT
POD1,POD2
PC control
Serial/Parallel
IC4
uart
BOVR
int
FINAL UNIT
CONTROL UNIT
PLL/DDS
IC500~IC502
Serial/Parallel
IC10,IC15,IC16
DAC
IC13
SM, VSFM, VSRM
SS, KEY, KYS
a/d
TX-RX UNIT
CPU
IC5
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).
Fig. 9 Reset circuit
Vcc
67
26
3
7
2
1
RESET
D1
5V
BA1
C34
IC3
Reset IC
IC5
CPU
Vcc
4.35V
2.15V
RESET RESET
td
Fig. 8 Control block diagram
CIRCUIT DESCRIPTION