TK-8302/8302H
14
■
High-speed data (2-tone)
The demodulated signal from the FM IC (IC500) is am-
plifi ed by the baseband IC and passes through a high-pass
fi lter to remove frequencies of 3kHz or more. The MCU digi-
tizes this signal and decodes the signal after receiving the
signal at pin 87 (HSDI).
■
MSK/ DTMF
The demodulated signal from the FM IC (IC500) will in-
put to the baseband IC (IC701), then the baseband IC will
decode and send the decoded information to MCU by the
data line.
The MCU then processes the decoded information.
IC701
Baseband IC
DTMF/MSK
decode
IC702
MCU
QT/DQT
LSDI
DTMF/MSK
decode data
REPLAY data
2-TONE
HSDI
IC500
FM IC
Fig. 15 Decode
7. Power Supply Circuit
When the power switch on the display unit is pressed,
the power port on the display unit which is connected to
port 17 (POWER), goes low, then port 52 (SBC) goes high,
Q719 turns on, SB switch (Q720) turns on and power (SB) is
supplied to the transceiver.
When the DC power is supplied to the transceiver, volt-
age regulator IC (IC707, IC706) will supply into the MCU
VDD and reset the voltage detect IC (IC709). IC709 will
generate signal (RESET) into the reset terminal on the MCU
(IC702) to carry out a power ON reset. Also, MCU (IC702) is
checking on port 91 (BATT). If DC power is less than about
8.5V, the transceiver is unable to power on.
When the DC power voltage deceases from normal volt-
age, the INT voltage detector IC (IC708) will set to high on
MCU port 18 (INT). If B line becomes less than about 8.5V,
MCU will send the backup data to EEPROM (IC703) and go
into STOP mode.
This circuit has an overvoltage protection circuit. If a DC
voltage of 16V or higher is applied to the base of Q710, this
voltage turns Q710 on and sets port 18 (INT) to low. As a re-
sult port 78 (SBC) is low, and turns Q719 and Q720 (SB) off.
Fig. 16 Power supply circuit
Q707
SW
Q720
SW
Q719
SW
IC707
AVR
D715
B
IC709
AVR
IC706
AVR
SBC
IGN
R792
R793
R851
R852
INT
5M
3.3M
BATT
IC702
MCU
POWER
SW
POWER
RESET
IC708
AVR
Q710
SW
SB
IGN
CIRCUIT DESCRIPTION