Features Low-Voltage (3-Volt) Supply 39 Programmable Sub-Audio Tones + NOTONE Meets MPT1306 and EIA 220 B High Voiceband/CTCSS Isolation Separate Sub-Audio and Rx/Tx Audio Paths and Filtering
Tx AUDIO INPUT Rx AUDIO INPUT Rx XTAL/CLOCK XTAL XTAL/CLOCK GENERATOR
Applications Mobile Radio Systems Community Base Stations "Sports Radio" (Japan) Sub-Audio Signalling and Selective Calling Status and Alarm Systems Amateur Radio
LOAD/LATCH SERIAL ENABLE 1/D5 SERIAL ENABLE 2/D4 SERIAL DATA/D3 SERIAL D1 D0 Rx/Tx PTL
LOGIC DECODE COMPARATOR REF. DECODE COMPARATOR INPUT
The a 3-volt, half-duplex predictive Continuous Tone Controlled Squelch System (CTCSS) encoder/decoder microcircuit. The FX365C has integral voice-band filtering for prefiltering of Tx audio and the rejection of the CTCSS tone in receive. Under ÁProcessor control, the FX365C will encode and decode any one of 39 sub-audio frequencies (+NOTONE) in the range to 250.3Hz. Tone frequencies and all functional commands can be loaded to the device in either pin-selectable 8-bit parallel or serial format. A separate, Rx/Tx voice-audio path is available with a highpass (sub-audio reject) filter automatically placed in the relevant or Tx voice line. The Rx sub-audio (CTCSS) path contains a (selected tone frequency) bandpass filter and period detector providing a logic level output (Rx Tone Detect) to indicate a successful decode operation. Rx "Press to Listen" (PTL) and Tx "Squelch-Tail Elimination" functions are available in both command loading modes. The squelch-tail elimination function will provide (Tx tone) phase-reversal to minimise the annoying audio outputs that occur at the receiver on completion of a transmission. Tone frequencies and filter accuracies are maintained by an on-chip 1.0MHz clock oscillator employing an external crystal or clock pulse input. The FX365C, which exhibits high audio and subaudio performance with low falsing, is available in 24pin DIL and small outline SMD packages.
VDD: Positive supply rail. A single stable supply is required; levels and voltages within the FX365C are dependent upon this supply. This pin should be decoupled to VSS by a capacitor located close to the pin.
Xtal/CIock: Input to the on-chip inverter; used with a 1.0MHz Xtal or external clock source.
Xtal: Output of the on-chip clock oscillator inverter.
Load/Latch: Controls 8 on-chip latches and is used to latch Rx/Tx, PTL, - D5. This pin is internally pulled to VDD. A logic `1' applied to this input places the 8 latches into a 'transparent' mode. A logic `0' applied to this input places the 8 latches into the `latched' mode. In parallel mode data is loaded and latched by a logic to `0' transition (see Figure 4a). In serial mode data is loaded and latched to `0' strobe pulse on this pin (see Figure 4b).
D5/Serial Enable 1: Data input D5 (Parallel Mode); Serial Enable 1 (Serial Mode). A logic `l' applied to this input, together with a logic `0' applied to D4/Serial Enable 2, will put the device into 'Serial Mode' (see Figure 4b). This pin is internally pulled to VDD.
D4/Serial Enable 2: Data input D4 (Parallel Mode); Serial Enable 2 (Serial Mode). A logic `0' applied to this input, together with a logic `1' applied to D5/Serial Enable 1, will place the device into `Serial Mode' (see Figure 4b). This pin internally pulled to VDD.
D3/Serial Data: Data input D3 (Parallel Mode); Serial Data Input (Serial Mode). In Serial Mode this pin becomes the serial data input for - D0, Rx/Tx, PTL (see Figure D5 is clocked-in first and PTL last. This pin internally pulled to VDD.
D2/Serial Clock: Data input D2 (Parallel Mode); Serial Clock Input (Serial Mode). In Serial Mode this pin becomes the Serial Clock input. Data is clocked on the positive-going edge (see Figure 4b). This pin is internally pulled to VDD.
D1: Data input D1 (Parallel Mode); Not Used (Serial Mode). This pin is internally pulled to VDD.
D0: Data input D0 (Parallel Mode); Not Used (Serial Mode). This pin is internally pulled to VDD.
Decode Comparator Ref. (I/P): Internally biased or 2VDD/3 via 1.0M resistors depending on the logical state of the Tone Decode Output pin, this input provides the decode comparator reference voltage; switching of bias voltages provides hysteresis to reduce 'chatter' under marginal conditions. Tone Decode Output = logic `1' will place this input to 2VDD/3 bias, a logic `0' will bias this input to VDD/3.
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).
Decode Comparator Input: The inverting input of the Decode Comparator. This pin to be connected to the Rx Tone Detect pin via external integrating components as shown in Figure 2.
Rx Tone Detect (O/P): In the Rx mode this output will to a logic `1' during a successful decode (Table 1). This pin to be connected to the Decode Comparator Input via the external integrating circuitry as shown in Figure 2.
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 a VDD/(2-0.7)V bias or open-circuit as described in Table 1.
Rx/Tx: This input (Parallel Mode) selects 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 VDD via a 1M 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.
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 In Tx Mode this pin is biased VDD/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 VDD/2. VBIAS: The output of the on-chip analogue bias circuitry. Held internally at VDD/2, this pin should be externally decoupled to VSS. 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 VDD/2. Rx Audio Input: The input to the Voice Audio high-pass filter in the Rx Mode. This pin is internally biased to VDD/2. Tone Input: The input to the CTCSS tone detector and is internally biased to VDD/2.