3012—Brief description
NGT Transceiver System Technical Service Manual 301
General information
DSP modem
Data modulation and demodulation is accomplished in firmware by a 32-bit DSP. Data
compression may also be enabled, if required. 2400 bps, 16-channel QPSK modulation
is used to provide up to 1475 bps effective uncompressed data rate.
Transceiver interface
The transceiver interface provides the modem with a switched supply rail. PTT, SCAN,
BUSY and QUIET control lines are implemented through dedicated hardware signals. A
CICS RS232 serial interface provides for additional communications between the
transceiver and the modem. Transmit and receive analog audio signals are transformer-
isolated and interfaced to the DSP via a CoDec, which contains an ADC and a DAC.
Terminal interface
Digital data exchange is facilitated through a conventional RS232 terminal interface,
which is fully electrically isolated to minimise possible earth problems. This is interfaced
to the DSP via a dual asynchronous communication element.
NOTE
The information in this section should be read in conjunction with the
block diagram 03-01080.
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