Icom IC-24AT Service Manual page 10

3-6-2
I/O
EXPANDER
1C
PORT
ALLOCATIONS
IC1 (lO
UNIT)
PORT
No.
PIN
No.
TERMINAL
NAME
DESCRIPTION
Q17
4
VCPC
Outputs
power saver
signal
to
cut the loop
filter
from the
VHP
PLL
1C.
Q18
5
UCPC
Outputs
power
saver signal
to cut the loop
filter
from
the
UHFPLLIC.
Q19,
Q20
6,
7 P01,
P02 Output
RF
output
power
selecting
signal.
Q21
14
V5C Becomes "LOW" when
selecting the
VHF
band.
This
port
is
controlled with
the
power
save
function.
Q22
13
U5C
Becomes "LOW" when
selecting the
UHF
band.
This port
is
controlled with
the
power saver
function.
IC2
(lO
UNIT)
PORT
No.
PIN
No.
TERMINAL
NAME
DESCRIPTION
Oil
6
UBAN
Becomes "LOW" when
the
UHF
band
is
selected.
012
7
TR5
Becomes "HIGH"
while
transmitting
and "LOW"
while receiving.
Q14
13
VT5 Becomes "LOW"
while
transmitting
in
the
VHF
band.
015
12
UTS Becomes "LOW"
while
transmitting
in
the
UHF
band.
016
11
T+5 Becomes
"HIGH"
while
transmitting.
IC6
(LOGIC
UNIT)
PORT
No.
PIN
No.
TERMINAL
NAME
DESCRIPTION
03
6
AFON Becomes
"HIGH"
to
open
the
squelch
for
beep
tone.
04
7
RMUT
Becomes
"HIGH"
to cut
the
AF
signal while
beep
tone
emits.
05
14
MICM
Becomes
"HIGH"
to
mute
the
microphone
input.
06
13
TXLED Becomes
"HIGH"
to
light
up
DS4
in
red while trans-
mitting.
3-6-3
S-INDICATOR
COMPARATOR
CIRCUIT (LOGIC
UNIT)
The
CPU
indicates
the
2nd
IF
signal level
as the
S-indicator
(S-meter)
to
the
LCD
(DS1)
when
the
SIN
port
(pin
2)
is
at
"LOW."
The
S-indicator signal
coming
from
the
DET
UNIT
is
applied
to
the
meter comparator
(IC2, pin 3).
Pin
2
of
the meter
comparator
receives
a counting
signal
from
the
CPU
(pins
3-6).
The
counting signal
is
increased step by
step.
The
comparator
(pin
1) is
at
"HIGH" when
the counting
signal
is
lower than the
S-indicator signal
and
becomes "LOW"
when
the counting
signal
is
higher than the S-indicator
signal.
When
the
comparator
(
IC2
,
pin
1
)
becomes
"LOW,"
the
CPU
detects that the signal strength level
is
the
same
as
the
counting
signal
level,
and
indicates the counting signal to
the
LCD.
S-INDlCATOR CIRCUIT
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3-5