Radyne OM20 Specifications download pdf (Page 47)

DMD1050 Satellite Modem Board Theory of Operation

3.14 Asynchronous Overhead Operation (J1)

This port is also dedicated for ES-ES Communications. The port may be configured for a number

of Asyncrounous communications protocols. Protocol supported are Standard IBS ES-ES,

Enhancd Asyncrouns and SCC. Overhead data to/from the UIM is routed to/from the

framer/deframer. This port may be configured to support either RS-232 or RS-485 signal levels.

The baud rate and protocol can be selected 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 termed 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 t0 through-

Data Ratio.

IBS 1/15 framing supports two Asnchrounous protocols.

For Regular Async: (ES to ES), the Baud Rate is approximately 1/2000 of the Data

Rate listed in Table 3-3.

For Enhanced Async: (Radyne Proprietary Async.), the Baud Rate is selectable, but

Data Rate is limited. Refer to 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 utilize 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 3-4. The “RS-485” Setting controls the output

into tri-state when the modem is not transmitting data, allowing multiple modem outputs to be

connected together.

MN-DMD1050 3–25

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Radyne OM20 Specifications Page 47