Icom IC-730 Maintenance Manual page 15

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inverter, then Pin6 of 1C3 as a switching signal. The other
waveform-shaped signal is output from pin3 of IC2 and
differentiated by C12 and Rl0, then fed to pinl of IC3,
inverter. The output signal from pin3 of IC3 is also dif-
ferentiated by Cll and R9, then fed to pins 5 and 12 of
1C3. To the other gates of 1C3, the switching signal is
applied and controlled the differentiated signals. The
output signals from pins 4 and 11 of 1C3 are fed to 2-
input NOR gate of IC3 and combined as the UP signal.
This UP signal is fed to CP terminal of IC5, flip-flop, and
it holds the output terminal, pin 13, H-Ievel when the UP
signal is present. This H-Ievel signal is then fed to B3
terminal of the CPU, and the CPU processes to increase
the operating frequency. When the tuning control is
turned counterclockwise, the B3 terminal is maintained in
the .L-Ievel.
Two differentiated signals at C12 and Cll are fed to pins
5 and 6 of IC2, OR gate, and combined signal is ~utPut
from pin4. The rotary encoder outputs 50 pulses per
revolution, while pin4 of IC2 outputs both leading edge
and trailing edge, resulting in an output of 100 pulses per
revolution. This output signal is fed to a counter of 3-bit,
consisting of 1C4 and a half of IC5.
This counter is capable of counting a maximum of 7
pulses, and serves as a timing buffer between the encoder
and the display in relation to reading by the CPU.
If
there
is any output at the counter, the output of the diode OR
gate, consisting of 05 throug, 07, becomes H-Ievel, input
to inverter, IC8, then input to the INT terminal of the CPU
with its level inverted to L-Ievel. This terminal is a priority
terminal which gives priority to sensor processing by
stopping other operations. In the priority routine, counter
data and up-down data fed to BO throug, B3 terminals
are read by the CPU, performing in this way all operations
related to sensor processing.
Immediately after the sensor data have been read, a reset
pulse is put out from IlJ terminal, and the pulse is differ-
entiated by C5 and R46, then fed to clear terminals of
the counter and up-down latch to clear them.
The up-down control circuit consisting of 03, 04, R16
through R21, C17 throug, C21, etc., provides frequency
control from the up-down switches on the microphone.
When the UP or DOWN button is depressed, the multi-
vibrator,
03, oscillates and pulses are fed to pin6 of IC4,
and the 3-bit counter counts the pulses the same as the
pulses from the rotary encoder.
After processing, the CPU outputs frequency data for the
PLL from the port E. This data is a 4-bit parallel data and
it is output in sequence according to its digits. The port E
also output frequency data for the display with time
sharing. This data is 4-bit parallel and 8-digit data. FO and
F2 terminals output clock pulses for the display and Fl
terminal outputs clock pulse for the PLl. Data for 1kHz
and lower digits are output from the ports C and 0, and fed
to DIA converter consisting of R35 through R43 to convert
into a analog signal. This analog signal is fed to the 2nd
3-8
local oscillator in the 2nd IF unit to get 10Hz step fre-
quency resolution.
3 - 4 DISPLAY UNIT
This unit is composed of DS1 display tube, ICl driver IC
and DC-DC converter for the display tube and negative
voltage source.
The frequency data is fed to pins 2 through 5, input port S,
and timing control pulse is fed to pin 15. After processing,
segment data is put out from pins 16 throug, 22 with digit
control signal put out from pins 6 through 11. These signals
are fed to the display tube and light the tube with dynamic
lighting.
The DC-DC converter is composed of 01, L1, Rl through
R3, Cl through C4, 01 through 04, etc. This converter
generates a negative voltage and filament voltage for the
display tube, and -5V for the AGC circuit and operational
ampl ifiers.
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