Pin Number
FX465 D5
13
Function
Rx Tone Decode
(O/P): The gated output of the on-chip Decode Comparator.
This output is used to gate the Rx Audio path. A logic ‘0’ on this pin indicates a successful decode and
that the ‘Decode Comparator In’ pin is more positive than the ‘Decode Comparator Ref.’ input (see
Table 1).
14
Decode Comparator In:
The inverting input of the Decode Comparator. This pin is normally
connected to the integrated output of the Rx Tone Detect pin.
15
Rx Tone Detect
(O/P): In the Rx mode this output will go to a logic ‘1’ during a successful decode
(Table 1). This must be externally integrated to control response and deresponse times (Figure 2).
16
Tx Tone Out:
The CTCSS sinewave output appears on this pin under the control of the Rx/Tx pin.
This output, when not transmitting a sub-audio tone, may be biased to V
DD
/2 as described in Table 1.
17
Rx/Tx:
This input (Parallel Mode) selects Rx or Tx modes (see Figure 2). Logic ‘1’ = Rx;
logic ‘0’ = Tx. In Serial Mode this (Rx or Tx) function is serially loaded. This pin is internally pulled to
V
DD
via a 1MΩ resistor.
PTL:
A dual-function input. In parallel Rx mode this pin operates as a “Push To Listen” function by
enabling the Rx audio path, thus overriding the tone-squelch function.
In the parallel load mode, Tx operation this input reverses the phase of the transmitting CTCSS tone
(squelch tail elimination). In the serial load mode (Rx and Tx) these functions are serially loaded.
Internal pull-up to V
DD
.
Rx Audio Out:
The high-pass filtered ‘Received Audio’ output. This pin outputs audio when Rx Tone
Decode = ‘0’, or PTL = ‘1’ or when ‘Notone’ is programmed (Table 2). In Tx Mode this pin is biased to
V
DD
/2.
Tx Audio Out:
The high-pass filtered ‘Transmit Audio’ output. In Tx mode this pin outputs audio
present at the Tx Audio input by opening the Tx audio path. In Rx mode this pin is biased to V
DD
/2.
V
BIAS
:
The output of the on-chip analogue bias circuitry. Held internally at V
DD
/2, this pin should be
externally decoupled to V
SS
via a capacitor.
Tx Audio In:
The Tx Audio Input pin. Tx voice-band audio may be prefiitered, using the audio path,
thus helping to avoid talk-off due to the intermodulation of speech frequencies with the transmitted
CTCSS tone. This pin is internally biased to V
DD
/2.
18
19
20
21
22
23
Rx Audio In:
The input to the audio high-pass filter in the Rx Mode.
This pin is internally biased to V
DD
/2.
Tone In:
The input to the CTCSS tone detector; this input is internally biased to V
DD
/2.
24
3
CMLMICRO [ CML MICROCIRCUITS ]
