Comtech EF Data SDM-650B - Manual (Page 62)

Configuration SDM-650B Satellite Modem
3–20 Rev. 5
3.2.3 DS-1 Interface
3.2.3.1 Functional Description
The DS-1 digital interface (Figure 3-6) provides level translation, buffering, and
termination between the internal modem signals and the DS-1 DTE interface on the rear
panel.
SWITCH 1
Figure 3-6. DS-1 Interface Card
The DS-1 standard is defined in Bell System Publication 62411.
Refer to Figure 3-7 for a functional block diagram of the DS-1 interface.
The DS-1 is a single data rate interface. The interface operates at 1.544 Mbit/s, normally
referred to as the “T1” rate. This interface is also unique in that no clock signals are
provided.
The clock information is provided in the data signal through the data encoding method
used, Alternate Mark Invert (AMI). In this method, a mark is transmitted as a positive or
negative pulse, one-half the width of the data-bit time. Each consecutive mark has the
opposite sign of its predecessor. Spaces are transmitted as an all-zero voltage.
In order to provide a clear channel (i.e., a channel in which an indefinite number of 0s
can be transmitted), B8ZS encoding and decoding are provided. This allows the modem
to interface with DTE utilizing B8ZS coding. B8ZS coding is enabled by an on-board
jumper (SW1-1). SW1-1 in the open position enables the B8ZS encoder and decoder.
SW-1 in the closed position disables the B8ZS encoder and decoder, and the DS1
interface will operate in AMI.