Comtech EF Data SDM-300A, Installation And Operation Manual

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SDM-300A Satellite Modem Options
Rev. 4 A–19
A.1.4 Asynchronous Interface/AUPC
Note: If required, refer to Section A.3 for installation of the overhead interface PCB.
The asynchronous (ASYNC) interface option provides the interface for terrestrial data
and a single ASYNC overhead channel. Typically used for earth-station-to-earth-station
communication, the overhead channel is MUXed onto the data and transmitted at an
overhead rate of 16/15 of the main channel. The AUPC feature works with the ASYNC
option to allow remote communication between a local modem and a remote modem.
Refer to Figure A-5 for a modem block diagram with the ASYNC/AUPC interface
option.
G.703, EIA-422, or V.35 interfaces are available for terrestrial data input and output.
These interfaces can be selected via the front panel.
EIA-485 or EIA-232 interfaces are available for ASYNC channel input and output. These
interfaces can also be selected from the front panel. Fixed 1/15 overhead is added to the
data when an ASYNC channel is being used. With the ASYNC channel enabled, the
terrestrial data rate can be from 8 to 2048 kbit/s. The ASYNC channel I/O protocol can
be as follows:
Baud 110 to 38400
Data Bits 5 to 8
Parity odd, even, or none
Stop Bits 1 or 2
Note: Certain combinations of baud rate, data rate, parity, and stop bits will limit the
maximum baud rate allowed for continuous throughput based on terrestrial data rate.
ASYNC overhead is a 1/15 rate overhead channel composed of the following:
•
Framing information
•
EIA-232 or EIA-485 data
•
Valid data flags
•
AUPC information (if installed)
•
Parity bits
The rate of asynchronous data transfers may be selected by the operator, with the
maximum rate available limited to 1.875
%
of the synchronous data rate.
Note: The asynchronous overhead structure is an Comtech EFData standard, and is not
compatible with IBS or IDR overhead formats.