Codan NGT 2010 RF Technical & Service Manual page 727

3012—Technical description
User Connector PCB
Transceiver interface
Drawing
The data modem and the transceiver are interfaced through connector P1. This interface
also provides power to the data modem via a filtering inductor (L1) and a polarity-
protection diode (D1). This is a Schottky diode to ensure minimum voltage drop, thereby
maximising efficiency and minimising overall current drain.
Power is fed through to the main DSP Modem PCB via connector P2.
The transceiver interface also supports transmit/receive audio, and PTT, SCAN, BUSY
and QUIET lines, which allow control between the data modem and the transceiver.
Transistor logic is used to interface these signals to IC107 on the DSP Modem PCB.
These functions connect to the DSP Modem PCB via connector P3.
Serial ports
Drawing
The User Connector PCB also performs interfacing of the serial ports.
A conventional charge-pump RS232 driver (IC3) drives the CICS transceiver interface.
IC1, IC4, V14 and V15 combine to provide a more elaborate, fully optically isolated
serial interface to a PC or data terminal equipment. Optical isolation on this interface is
provided to eliminate possible problems with HF signals entering the PC, or large
currents flowing in the grounds of serial cables.
A stand-alone isolated DC−DC converter module (IC1) generates isolated approximate
+5 V and +10 V rails. These feed an RS232 driver (IC4), which uses an internal charge
pump to generate a negative rail. Therefore, the TTL level signals from the DSP
Modem PCB pass from connector P6, through the opto-couplers and IC4, to the terminal
interface via P4.
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NGT Transceiver System Technical Service Manual