Comtech EF Data SDM-2020, Installation And Operation Manual

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SDM-2020 Satellite Demodulator Data Interfaces
Rev.3 A–21
A.4 ASI/RS-422 (Asynchronous Serial Interface and Serial Data
Interface)
The following paragraphs describe the ASI/RS-422 Data Interface.
A.4.1 Applicable Documents
Applicable specifications, as referenced herein, include:
TM1449 Interfaces for CATV/SMATV Headends and Similar Professional Equipment
RS-422 Electrical Characteristics of Balanced Voltage Digital Interface Circuits
EIA-530 High Speed 25-Position Interface for Data Circuit - Terminating Equipment
A.4.2 Description
This data interface is a plug-in module that inserts into the rear of the SDM-2020
modulator or demodulator chassis. It provides physical and electrical connection between
the external terrestrial circuit and the internal circuitry of the modulator or demodulator.
The plug-in interface has full duplex capability but is automatically configured for
simplex-transmit or simplex-receive operation.
The ASI/RS-422 interface combines two electrical and physical interfaces into a single
assembly. The ASI section provides a DVB-compliant interface with BNC connectors,
while the RS-422 section supports serial communications through a standard 25-pin D
connector per EIA-530. Operation for either ASI or RS-422 is selected by programming
the unit from the front panel keypad/LCD or from the remote port. Only one of the
interface types is active at a time. Figure A-5 is a block diagram of the interface; Figure
A-6 is a drawing of the ASI module assembly.