![background image](http://html.mh-extra.com/html/icom/ic-756pro-iii/ic-756pro-iii_service-manual_612292018.webp)
3 - 12
3-7-4 INPUT EXPANDER ALLOCATIONS
(1) DISPLAY board; IC411
(2) MAIN-A unit; IC3652
3-7-5 OUTPUT EXPANDER ALLOCATIONS
(1) PLL unit; IC1
(2) PLL unit; IC101
(3) PLL unit; IC401
1
5
12
13
14, 15
Input port for the [RIT], [
∆
TX] and
[CLEAR] switches.
Input port for [UP] and [DN] switches
of the connected microphone.
Input port for the [DUALWATCH],
[CHANGE], [V/M] and [M/S] switches.
I n p u t p o r t f o r t h e [ T U N E R ] ,
[MONITOR], [NB] and [NR] switches.
Input ports for the multi-function
switches.
KI4
MUDK
KI3
KI0
KI1, KI2
Pin
Port
Description
number
name
11
12
13
14
16
17
18
Input port transmission status for CW
Input port for RTTY decode data.
Input port for the KEY signal from the
connected AH-3.
Low : While tuning or tune NG
Input port for AH-3 connection detec-
tion.
High : When AH-3 is connected.
Input port for interrupting signal
from audio recoder.
Input port for address clock signal
from audio recoder.
Input por t for busy signal from
t h e i n s t a l l e d U T- 1 0 2 S P E E C H
SYNTHESIZER.
CTFL
RTDT
EKEY
TCON
VINT
VRAC
SBSY
Pin
Port
Description
number
name
66
68
70
71
73
74
75
Outputs the marker mute switch
(IC192) control signal.
High :
When the marker ON is select-
ed.
Outputs LO mute switch (Q361) con-
trol signal.
Low : Muted
Outputs bandpass filter select switch
(Q351) control signal.
High :
When less than 8 MHz is dis-
played on the main band.
Outputs the LO switch (Q121) control
signal.
High :
While 45.0–60.0 MHz band is
displayed on the main band.
Outputs the LO switch (Q122) control
signal.
High :
While 20.0–44.999999 MHz band
is displayed on the main band.
Outputs the LO switch (Q123) control
signal.
High :
While 8.0–19.999999 MHz band
is displayed on the main band.
Outputs the LO switch (Q126) control
signal.
High :
While 0.03–7.999999 MHz band
is displayed on the main band.
MAKS
PAMT
PAFS
VA4S
VA3S
VA2S
VA1S
Pin
Port
Description
number
name
68
70
71
73
74
75
Outputs LO mute switch (Q661) control
signal.
Low : Muted
Outputs bandpass filter select switch
(Q651) control signal.
High :
When less than 8 MHz is dis-
played on the main band.
Outputs the LO switch (Q421) control
signal.
High :
While 45.0–60.0 MHz band is
displayed on the main band.
Outputs the LO switch (Q422) control
signal.
High :
While 20.0–44.999999 MHz band
is displayed on the main band.
Outputs the LO switch (Q423) control
signal.
High :
While 8.0–19.999999 MHz band
is displayed on the main band.
Outputs the LO switch (Q426) control
signal.
High :
While 0.03–7.999999 MHz band
is displayed on the main band.
PBMT
PBFS
VB4S
VB3S
VB2S
VB1S
Pin
Port
Description
number
name
4
5
6
7
12
13
14
Outputs strobe signals to DDS IC
(IC101) for the 1st LO PLL A circuit.
Outputs strobe signals to PLL IC
(IC381) for the 1st LO PLL A circuit.
Outputs strobe signals to DDS IC
(IC401) for the 1st LO PLL B circuit.
Outputs strobe signals to PLL IC
(IC681) for the 1st LO PLL B circuit.
Outputs strobe signals to DDS IC
(IC701) for the 3rd LO PLL circuit.
Outputs strobe signals to PLL IC
(IC901) for the S2 LO PLL circuit.
Outputs strobe signals to DDS IC
(IC801) for the S3 LO PLL circuit.
PST1
PST2
PST3
PST4
PST5
PST6
PST7
Pin
Port
Description
number
name