Realistic HTX-100 Service Manual page 10

2. Microcomputer peripheral circuits
A 4-bits single chip microcomputer is used with peripheral circuits shown below:
~--~
UC1208
L----L--L....-..----1
CPU
loA
ODE OUT(SSB/CN)
- - - - t
STOP
RESET
vee
o
Y401
T
CLOCK
With the power turned on the RESET circuit (IC404, 0402, 0403) operates and allows the microproces-
sor to transfer PLL data and LCD display data to each IC.
A signal from the pulse switch 8613 is waveshaped in IC403 and then applied to the microprocessor to
prevent erroneous count operation.
In the transmit mode, PTT IN (pin 41) goes Low level and TX OUT (pin 56) goes Hi level. Then, 0401 oper-
ates and the unit enters the TX mode.
In the transmit mode, MUTE output (pin 57) goes Hi level and the AF IC is muted. However, in the CW
mode the MUTE output is released, thus outputting the CW monitor sound.
C413 (super capacitor) relates to memory back-up time and holds the memory contents for about 17
months.
Moreover, by connecting a power source to the BATTERY terminal the memory backup will be assured
regardless of power switch of the unit.
The KEY matrix consists of seven switches, 3 rows by 3 columns as shown below .
DOWN UP
.. ODE
UC1208
6 9 10
Operation of keys varies voltage level (Hi or Low) on the matrix and with this variation respective function
will be actuated (as programmed in the microcomputer). When operating each key, 2kHz beep tone is
generated at pin 27 for 50ms and applied to the AF power amplifier.
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