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MC145444P Scheda tecnica(PDF) 6 Page - Motorola, Inc |
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MC145444P Scheda tecnica(HTML) 6 Page - Motorola, Inc |
6 / 12 page MC145444 MOTOROLA 6 TxA2 Inverting Transmit Analog Carrier Output (Pin 17) This pin is the line driver inverting output. The signal is equal in magnitude, but 180 ° out of phase with the TxA1 (refer to TxA1). RxA Receive Signal Input (Pin 19) This pin is the receive signal input. The pin has an input impedance of 50 k Ω (min). RxGC Receive Gain Adjust (Pin 20) This pin is used to adjust the receive buffer gain. To adjust the gain, the signal from the RxBO through a divider is added as a feedback. This pin may be held open when the gain adjustment is not needed. RxBO Receiver Buffer Output (Pin 1) This pin is the receive buffer output. DSI Driver Summing Input (Pin 16) This pin is the inverting input of the line driver. An external signal is transmitted through an external series resistor RDSI. The differential gain GDSI = (VTXA1 – VTXA2)/VDSI is deter- mined by the following equation. GDSI = – 2Rf / RDSI, Rf ≈ 20 kΩ DSI should be left open when not used. CDA Carrier Detect Level/CPTD Level Control (Pin 4) The carrier/call progress tone detect level is programmed with a CDA pin voltage. When this pin is held open, the CDA voltage is set to 1.2 V with an internal divider. The detect level is set at – 44 dBm (typ) for off to on, and – 47 dBm (typ) for on to off. The minimum hysteresis is 2 dB. This pin has a very high input impedance so it should be connected to GND with a 0.1 µF capacitor to keep it well regulated. An external voltage may be applied to this pin to adjust the carrier detect threshold. The following equations may be used to find the CDA voltage required for a given threshold voltage. VCDA = 245 × Von VCDA = 347 × Voff FTLC Filter Test (Pin 2) This pin is a high–impedance filter output. It may be used to check the receive filter. This pin also may be used as a demodulator input. In normal operation, this pin is connected to the GNDA through a 0.1 µF bypass capacitor. This pin handles very small signals so care must be used with the capacitor’s wiring. TLA Transmit Carrier Level Adjust (Pin 6) This pin is used to adjust the transmit carrier level that is determined by the value of the resistor (RTLA) connected between this pin and GND. The maximum transmit level is obtained when this pin is connected to GND (RTLA = 0). SERIAL INTERFACE The following six functions are set up with the 15–bit serial data. T3 T2 T1 T0 CD1 CD0 A2 A1 A0 TONE FREQUENCY : CARRIER DETECT TIME : CHANNEL : SQ TRANSMIT SQUELCH : FUNCTION MODE : TRANSMIT ATTENUATOR : CH A3 M2 M1 M0 Figure 3 presents the 15–bit serial data timing, starting with the carrier detect time, CD1, followed by the channel, the tone frequency, the transmit squelch, the transmit attenu- ator, and the function mode. This data is loaded into the inter- nal shift register at the rising edge of the SCK signal and latched at the falling edge of the ENB signal. FUNCTION MODE Modes are selected from the following 3–bit data (M2 – M0, see Table 1). Table 1. Function Mode Truth Table M2 M1 M0 Function Mode 0 0 0 FSK 0 0 1 Analog Loopback 0 1 0 CPTD 0 1 1 Answer Tone 1 0 0 DTMF 1 0 1 Single Tone 1 1 0 Power–Down 1 1 1 1 Power–Down 2 The following paragraphs describe each function. Table 2 presents each output status. FSK Mode The transmitter and the receiver work as a FSK modula- tor/demodulator. The SD pin output is the carrier’s detect signal. Analog Loopback Mode TxA1 connects to the receiver internally and FSK signals are demodulated. The frequency of the receiver is set up with the same frequency as the transmitter. The SD pin output is the carrier detect signal. An IC self test is supported with this function. CPTD Mode The receiver detects a 400 Hz call progress tone. The detect signal comes from the SD pin. The transmitter is disabled. |
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