Pin Number
FX375J FX375LG
FX375LH FX375L
15
12
Function
Tx Tone Output :
This is the buffered, programmed CTCSS tone sinewave output in
Tx. During Rx and Notone operation this output is held at V
BIAS
. See note "g," page 7 with
reference to capacitive load limits of this output.
V
BIAS
:
This bias pin is set internally to V
DD
/2. It must be externally decoupled using a
capacitor, C
8
, of 1.0µF (minimum) to V
SS
, see Figure 2.
Filter Output :
The Input Audio Bandpass Filter output, this pin must be connected to
the Balanced Modulator Input via a capacitor, C
6
, and decoupled to V
SS
by C
10
, see
Figure 2.
Balanced Modulator Input :
The input to the Balanced Modulator, this pin must be
connected to the Filter Output via a capacitor, C
6
, see Figure 2.
Rx Audio Output :
Outputs the received audio from a buffered output stage and is held
at V
BIAS
when in Tx.
Tx Audio Output :
The output of the audio path in the Tx mode and is held at V
BIAS
when in Rx.
Rx Audio Input :
The Audio input pin for the Rx mode. Input signals should be a.c.
coupled via an external capacitor, C
4
, see Figure 2.
Tx Audio Input :
This is the voice input pin for the Tx mode. Signals should be a.c.
coupled via an external capacitor, C
3
, see Figure 2.
PTL :
The "Press To Listen" function input, in the receive mode a logic '0' enables the
Rx Audio Output directly, overriding tone squelch but not intercepting a private
conversation. In the transmit mode a logic '0' reverses the phase of the Tx Tone Output
for "squelch tail" reduction (see Table 1), this function, in Tx, should be accurately
applied by a timing circuit to ensure correct system operation.
Control :
This input, with Load/Latch, selects the operational mode of Rx/Tx and
Private Enable functions, see Table 3.
Rx/Tx :
Selects the receive or transmit mode (Rx = '1', Tx = '0') and can be loaded by
serial or parallel means, as described in Table 3.
Private Enable :
This input selects either Private or Clear modes (Clear = '1',
Private ='0'), and can be loaded by serial or parallel means, as described in Table 3. In
Rx this input could be taken from the Rx Tone Decode Output. This input has an internal
1MΩ pullup resistor.
Rx Tone Input :
The received tone input to the on-chip CTCSS decoder and should be
a.c. coupled via capacitor C
5
, see Figure 2.
V
DD
:
Positive supply rail. A single +5V power supply is required.
16
13
17
14
18
15
19
16
20
17
21
18
22
19
23
20
24
21
25
22
26
23
27
24
28
1
3
CMLMICRO [ CML MICROCIRCUITS ]
