Introduction - Comtech EF Data CDM-710 Installation And Operation Manual

12.1

Introduction

This data interface is a plug-in module that inserts into the rear of the modem chassis. It provides
physical and electrical connection between the external terrestrial device and the internal circuitry
of the modulator or demodulator. By convention, a modem is Data Communications Equipment
(DCE) where Tx data enters the data interface and Rx data exits it. The plug-in interface has full
duplex capability.
In addition, the module is automatically configured for simplex-transmit or simplex-receive
operation when the module is plugged into a simplex chassis configured for modulator only or
demodulator only operation. Slot 1 of the modem is filled with a data interface card first, and Slot
2 is assigned a blank panel or another interface depending upon configurations allowed at time of
order. (Slot 1 is located near the center of the rear panel, and Slot 2 is next to the outside edge.)
The CDI-60 is a HSSI Card data interface module that plugs into the rear of the modem. Figure
12.1 is a block diagram of the interface. The HSSI interface provides:
A single HSSI interface
Supports 188 byte MPEG-2 transport stream only
DCE Connection
 RT is derived from the received satellite clock and is provided to the DTE as a
 ST is equivalent to the modem transmit rate and is sourced to the terrestrial
 TT is treated as an incoming Transmit Clock. TT must be equal to the transmit
Chapter 12. CDI-60
receive data clock.
interface for use as a reference by the DTE.
data rate. The precision of TT must be </= 100ppm.
HSSI Interface
12–1