2 description – Comtech EF Data SDM-2020 User Manual

Page 146

SDM-2020 Satellite Demodulator

Revision 4

ASI/RS-422Data Interface

MN/SDM2020D.IOM

9–2

9.1.2 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 9-1 is a block diagram of the interface; Figure
9-2 is a drawing of the ASI module assembly.

ASI

RECOVERY

RECOVERY,

PROCESSING

AND

ASI/EIA

SELECTION

ASI

GENERATOR

LOOPBACK

LEVEL

TRANSLATORS

M&C

MODULATOR/
DEMODULATOR
INTERFACE

TERRESTRIAL
INTERFACE

TX
ASI

RX
ASI

BNC-F

DC
POWER

Figure 9-1. ASI/RS-422 Interface Block Diagram