Icom IC-725 Service Manual page 15

4-4-2 CPU (PLL UNIT)
The CPU (CS) contains an 8-bit CMOS CPU, 16k-byte ROM
and 256-byte RAM. The CPU controls operating
frequency, mode and the function display, etc. The
memory contents are stored in the CPU using a lithium
backup battery for more than 5 years.
The Icom СІ-У network system allows that the IC-725 сап
be remotely controlled by a personal computer using an
RS-232C signal line.
4-4-3 RIT CIRCUIT (PLL UNIT)
IC12 is an A/D converter which outputs 8-bit serial data
regarding analog input voltage. А voltage, controlled by
the [RIT] control, is applied to ІС12 pin 4 and the resulting
serial data is applied to the CPU matrix Ү4-> DB4.
4-4-4 KEY MATRIX
YO Y1 Y2 Y3 Y4
DBO
DB1
съм BUS
CHECK
‫א‬
LCD DRIVER‫‏‬
EM
ин! е
5 <
kHz
SQL
DB2
<
N
RIT (+49 | AM/FM
RIT DATA
<
083
084
[AH3] KEY
ON
DB5 3
a
DB6
MIC UP/DN
SPEED
TUNER
(THROUGH)
087
на. 7
[AH3] START
4-4-5 PARALLEL/SERIAL CONVERTER
(PLL UNIT)
IC11 is a parallel/serial converter IC. Parallel data from
the CPU are converted into serial data to transfer the PLL
N-data, DDS N-data, data for LCD driver, etc.
When the power is turned ON, the CPU also outputs
programmable divider data and a control signal for
universal ports to the PLL IC (IC13).
4-5 REGULATOR CIRCUITS
Either 8, 5 or —5 V DC are supplied from corresponding
regulator circuits. 8, 5 and —5 V DC are regulated at
the following circuits using 13.8 V DC.
(1) 5 V REGULATOR (PLL UNIT)
5 V DC are regulated by the three-terminal voltage
regulator (IC10).
(2) 8 V REGULATOR (MAIN UNIT)
8 V DC are regulated by the three-terminal voltage
regulator (IC14).
(3) —5 V REGULATOR (PLL UNIT)
IC6 generates a negative pulse-type voltage by converting
the DC input to AC voltages (approx. 6.7 kHz) as a
multivibrator. The voltage is rectified at D8 and D9,
regulated by a Zener diode (D10) and C13, and is then
applied to the MAIN UNIT.