Pin Number
FX365C
13
DW and J package styles.
Function
Rx Tone Decoder
(O/P): The gated output of the on-chip Decode Comparator.
This output is used to gate the Rx Audio path. A logic ‘0’ output on this pin indicates a successful
decode and indicates that the ‘Decode Comparator Input’ pin is more positive than the ‘Decode
Comparator Ref’ input (see Table 1).
14
Decode Comparator Input:
The inverting input of the Decode Comparator. This pin is to be
connected to the Rx Tone Detect pin via external integrating components as shown in Figure 2.
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 pin is to be connected to the Decode Comparator Input via the external integrating
circuitry as shown in Figure 2.
16
Tx Tone Output:
A low-impedance emitter-follower source, under the control of the Rx/Tx pin, of the
CTCSS sinewave. This output, when not transmitting a sub-audio tone, may be set to a V
DD
/(2-0.7)V
bias or open-circuit 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 via pin 7 (Serial Data) and this
pin not used. This pin is internally pulled to V
DD
via a 1MΩ resistor (Rx operaion).
PTL:
A dual-function input. In the parallel load mode, Rx operation: A logic ‘1’ provides a “Press To
Listen” function by overriding the tone-squelch and enabling the audio path.
In the parallel load mode, Tx operation: A logic ‘1’ provides a “Squelch Tail Elimination” function by
reversing the phase of the transmitting sub-audio tone; the phase reversal function should be applied
by a suitable timing circuit.
In the serial load mode (Rx and Tx) these functions are loaded via the serial data word at pin 7.
18
19
Rx Audio Output:
The high-pass filtered ‘Received Audio’ output. This pin outputs audio when Rx
Tone Decode = ‘0’, or PTL = ‘1’ or ‘Notone’ is programmed (Table 2). In Tx Mode this pin is biased to
V
DD
/2.
Tx Audio Output:
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
.
Tx Audio Input:
The Tx Audio Input pin. Tx voice-band audio may be prefiitered, using the Voice
Audio Path, thus helping to avoid talk-off due to the intermodulation of speech frequencies with the
transmitted CTCSS tone. The Tx Audio Path may also be used to pre-filter speech when employing
‘scramblers’ which could introduce noise into the low frequency band. This pin is internally biased to
V
DD
/2.
Rx Audio Input:
The input to the Voice Audio high-pass filter in the Rx Mode.
This pin is internally biased to V
DD
/2.
Tone Input:
The input to the CTCSS tone detector and is internally biased to V
DD
/2.
20
21
22
23
24
3
CMLMICRO [ CML MICROCIRCUITS ]
