Comtech EF Data SDM-2020, Installation And Operation Manual

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SDM-2020 Satellite Demodulator Data Interfaces
Rev.3 A–65
A.8 ASI/LVDS Data Interface
The plug-in module provides the physical and electrical interface between external
terrestrial data equipment and the modulator. The ASI/LVDS implements the two most
popular DVB Data interfaces. The data is input/output on a BNC female connector as an
800 mV signal with biphase mark encoding. A separate auxiliary connector provides fault
status.
A.8.1 Applicable Documents
Applicable specifications, as referenced herein, include:
•
EN 80053-9, Interfaces for CATV/SMATV Headends and Similar Professional
Equipment
A.8.2 Description
This data interface is a plug-in module that inserts into the rear panel of the chassis. The
data interface provides a physical and electrical connection between the external
terrestrial circuit and the internal circuitry of the unit. By convention, a modem is Digital
Communications Equipment (DCE) where transmit data enters the data interface and
receive data exits it. The data interface has full duplex capability but is automatically
configured for simplex-transmit or simplex-receive operation, depending upon whether it
is plugged into a modulator or demodulator chassis.
Figure A-20 shows the ASI/LVDS data interface block diagram. At a functional level, the
data interface has three ASI I/O ports. One port is LVDS interface and an auxiliary
connector. Transmitted data into the modulator enters the ASI/LVDS data interface at the
TX input as a synchronous serial data stream, while data received by a demodulator is
sent by the data interface at the RX outputs as a synchronous serial data stream. The ASI
data stream is a serial, high-speed 8B/10 encoded signal, while the outputs for modulator
and demodulator faults as well as input for control and transmission.