TK-7108
31
■
D/A Converter
The D/A converter (IC161) is used to adjust MO modula-
tion, 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 port 17
(POWER), goes low, then port 82 (SBC) goes high, Q32 turns
on, SB SW (Q31) turns on and power (SB) is supplied to the
radio.
When the DC power supplied to the radio, the voltage
regulator IC (IC33) supply into the CPU VDD and reset voltage
detect IC (IC34). IC34 will generate signal (RESET) in to the
reset terminal on the CPU (IC101) to carry out a power ON
reset. Also, CPU (IC101) is checking on port 91 (Battery Volt-
age). If DC power is less than about 9.5V, the radio is unable
to power on.
When the DC power voltage deceases from normal volt-
age, the INT voltage detector IC (IC35) will set to high on CPU
port 18 (INT) if B line will became less than about 9.5V. Then
CPU send to EEPROM (IC66) the backup data and go into
STOP mode.
This circuit has an overvoltage protection circuit. If a DC
voltage of 18V or higher is applied to the base of Q61, this
voltage turns Q61 on and turns Q32 and SB off.
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CIRCUIT DESCRIPTION /
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Fig. 16
Power supply circuit /
NS
