Logic Circuits - Icom IC-756PRO Service Manual

3-6-3 MAIN UNIT
LINE
Receive 8 V converted from the 14 V line and
R8V regulated by the R8V regulator circuit (Q601,
Q602, D601).
Transmit 8 V converted from the 14 V line and
T8V regulated by the T8V regulator circuit (Q611,
Q612, D611).
3-6-4 CTRL AND PLL UNITS
LINE
Common 5 V for the antenna tuner CPU (CTRL
unit; IC5) and the EEPROM (CTRL unit; IC6),
5V
converted from the 14 V line and regulated by
the +5 regulator circuit (CTRL unit; IC13).
Common 5 V for each of the PLL-A and PLL-B
circuits regulated from the 8 V line and regulated
5V
by the +5 regulator circuit (PLL unit; IC382: PLL-
A, IC682: PLL-B).

3-7 LOGIC CIRCUITS

3-7-1 BAND SELECTION DATA
(RF, CTRL AND PLL UNITS)
To select the correct bandpass, low-pass filters and VCOs
on the RF, FILTER and PLL units, the main CPU (MAIN unit,
IC3501) outputs the following band selection data via the I/O
expander (RF unit, IC901, IC902, CTRL unit, IC11) or DDS
IC (PLL unit, IC101, IC401) depending on the displayed fre-
quency.
IC901, IC902
Frequency
(RF unit)
[MHz]
BPF
0.003–1.599999 B0
1.6–1.999999 B1
2.0–2.999999 B2
3.0–3.999999 B3
4.0–5.999999 B4
6.0–7.999999 B5
8.0–10.999999 B6
11.0–14.999999 B7
15.0–19.999999
B8
20.0–21.999999
22.0–29.999999 B9
30.0–44.999999
B10W
45.0–49.999999
50.0–54.000000 B10
54.000001–
B10W
60.000000
The D/A convertor (MAIN unit, IC3751) output signal from
pin 7 is amplified at IC101b (pins 5–7) to obtain the band
voltage for external equipment via the [ACC 2] connector pin
4.
DESCRIPTION
DESCRIPTION
IC11 IC101 IC401
(CTRL) (PLL) (PLL)
LPF VCO-A VCO-B
L1S
VA1S VB1S
L2S
L3S
L4S
VA2S VB2S
L5S
L6S VA3S VB3S
L7
VA4S VB4S
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