TM-281A
9
■
D/A Converter
The D/A converter (IC705) is used to adjust the MO mod-
ulation, AF volume, TV voltage, FC reference voltage, and
PC POWER CONTROL voltage level.
Adjustment values are sent from the MCU 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 (Approx. 2.2V)
n: Serial data value from the microprocessor (MCU)
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 82 (SBC) goes high,
Q713 turns on, SB SW (Q714) turns on and power (SB) is
supplied to the radio.
When the DC power is supplied to the radio, the volt-
age regulator IC (IC713) is supplied to the MCU VDD and
reset voltage detect IC (IC714). IC714 will generate a signal
(RESET) into the reset terminal of the MCU (IC707) to carry
out a power ON reset. If DC power is less than approxi-
mately 9.5V, the radio is unable to power on.
When the DC power voltage deceases from the normal
voltage, the INT voltage detector IC (IC712) will set to high
on MCU port 18 (INT) if B line becomes less than approxi-
mately 9.5V. The MCU will then send the backup data to the
EEPROM (IC708) and enter stop mode.
This circuit has an overvoltage protection circuit. If a DC
voltage of 18V or higher is applied to the base of Q707, this
voltage turns Q707 on and will set to high on MCU port 18
(INT). The MCU will then send the backup data to the EE-
PROM (IC708) and enter stop mode. (See Fig. 16.)
Q714
SW
Q713
SW
Q707
SW
IC713
AVR
D712
D710
B
IC714
RST
SBC
R824
R825
INT
5M
IC707
MCU
POWER
SW
POWER
RESET
5M
IC712
INT
SB
Fig. 16 Power supply circuit
CIRCUIT DESCRIPTION
TX-RX UNIT (X57-8130-XX)
Ref. No.
Use / Function
Operation / Condition / Compatibility
IC1
PLL IC
Frequency control
IC2
Divider
Frequency divider
IC302
Power module
TX fi nal amplifi er
IC303
APC controller
TX power control
IC501
FM IC
FM detector/ 2nd mixer/ RSSI/
Noise amplifi er
IC703
OP amplifi er
MIC amplifi er/ IDC
IC704
OP amplifi er
Splatter fi lter
IC705
Digital
potentiometer
Frequency adjustment
Modulation balance adjustment
AF level adjustment
Backlight control
Modulation limit adjustment
TX power/ BPF control
RX signal level control
Ref. No.
Use / Function
Operation / Condition / Compatibility
IC706
OP amplifi er
Buffer amplifi er/ SUM amplifi er/
DC amplifi er/ 1/2 VCC
IC707
MCU
IC708
EEPROM
Tuning data/ Memory data
IC709
OP amplifi er
Audio fi lter
IC710
5V AVR
5C
IC711
8V AVR
8C
IC712
Voltage detection
MCU INT voltage detection
IC713
5V AVR
5M
IC714
Voltage detection
MCU reset voltage detection
IC715
Audio amplifi er
Audio fi nal amplifi er
IC901
LCD driver
Display control
Q1,2
Switching Charge
pump
Q3
RF amplifi er
PLL Fin
COMPONENTS DESCRIPTION