DMD1050TS Satellite Modem Board
Revision 1
Theory of Operation 3–29 MN-DMD1050TS
3.14 Asynchronous Overhead Operation (J3)
This port is dedicated for ES-ES Communications as well. You can configure the port for several
Asyncronous communications protocols. Protocols supported are Standard IBS ES-ES, Enhancd
Asyncronous and SCC. Overhead data to/from the UIM is routed to/from the framer/deframer.
You can configure this port to support either RS-232 or RS-485 signal levels.
You can select the baud rate and protocol from the Web Browser.
The Asynchronous Framing/Multiplexer is capable of multiplexing a relatively low speed overhead
channel onto the terrestrial data stream, resulting in a slightly higher combined or aggregate data
rate through the modem. The overhead channel is recovered at the far end. This added channel
is called variously: “An Overhead Channel”, ”Service Channel”, “Async Channel” or, in IESS
terminology, an “ES-to-ES Data Channel.” The basic frame structure used by the multiplexer is
that specified in the IESS-309 Standard, resulting in a 16/15 Aggregate to through-Data Ratio.
IBS 1/15 framing supports two Asnchrounous protocols.
• For Regular Async:
o (ES-to-ES), the Baud Rate is approximately 1/2000 of the Data Rate listed in
Table 3-3.
• For Enhanced Async:
o (Radyne Proprietary Async.), the Baud Rate is selectable, but Data Rate is
limited. See Table 3-3 for differences between Regular and Enhanced Async.
The maximum Baud Rate is 19,200 bps for IBS Async. Two software-controlled modes are
designed into the card to best use the available bits: Standard IBS ES-to-ES and IBS (Enhanced
Async).
The Async Channel can be set under software-control to either RS-232 or RS-485 mode. The pin
assignments for both modes are shown in Table 3-5. The RS-485 setting controls the output into
tri-state, when the modem is not transmitting data, allowing multiple modem outputs to be
connected.
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