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TK-7102
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The QT and DQT signals are output from QT/DQT of the
CPU (IC6) and summed with the external pin DI line by the
summing amplifier (IC4) and the resulting signal goes to the
D/A converter (IC3). The DTMF signal is output from DTMF
of the CPU and goes to the D/A converter (IC3). The signal
is summed with a MIC signal by the summing amplifier
(IC4), and the resulting signal goes to the D/A converter
(IC3).
The D/A converter (IC3) adjusts the MO level and the bal-
ance between the MO and QT/DQT levels. Part of a QT/
DQT signal is summed with MO and the resulting signal
goes to the VCOMOD pin of the VCO. This signal is applied
to a varicap diode in the VCO for direct FM modulation.
QT/DQT
IC6
CPU
IC4
DTMF
IC3
SUM
D/A
AMP
Fig. 14 Encode
Decode
• QT/DQT/DTMF
The signal (DEO) passes through two low-pass filters of
IC11, goes to QTIN of the CPU (IC6) to decode QT, DQT.
The DTMF signal is decoded by a dedicated IC (IC9) and the
resulting signal is sent to the CPU (IC6) as serial data.
IC11(2/2)
QTIN
IC6
SD
CPU
STD
ACK
DECO.
Fig. 15 Decode
14
CIRCUIT DESCRIPTION
TCXO
IC4
MOD
X1
SUM
TCXO
AMP
DI
IC3
D/A
VCO
MOD
IC11(1/2)
LPF
LPF
DEO
IC9
DTMF
D/A Converter
The D/A converter (IC3) is used to adjust MO modulation,
AF volume, TV voltage, FC reference voltage, and PC
POWER CONTROL voltage level.
Adjustment values are sent from the CPU as serial data.
The D/A converter has a resolution of 256 and the following
relationship is valid:
D/A output = (Vin – VDAref) / 256 x n + VDAref
Vin: Analog input
VDAref: D/A reference voltage
n: Serial data value from the microprocessor (CPU)
Power Supply Circuit
When the POWER switch on the display unit is pressed,
the power port on the display unit which is connected to
CPU port 18 (POWER), goes low, then CPU port 93 (SBC)
IC3
goes high, Q34 turns on, SB SW (Q42) turns on and power
PLL
(SB) is supplied to the radio.
This circuit has an overvoltage protection circuit. If a DC
voltage of 18 V or higher is applied to the power cable, D39
VCO
turns on and a voltage is applied to the base of Q38. This
voltage turns Q38 on and turns Q34 and SB off.
HT
B
Q16
IGN
SW
IC6
CPU
POWER
SW
Fig. 16 Power supply circuit
Q42
SW
Q34
SW
Q38
SW
SBC
5M
IC17
5M
AVR
POWER
IC15
RESET
RESET
Q18
INT
B
D39
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