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DMD50 Universal Satellite Modem
3.12.1 To Disable the ESC Backward Alarms
If the ESC ALARMS Port will not be used and the Backward Alarm Indications are to be disabled,
you must connect pins 10, 11, 22 and 23 to pin 1 (gnd) on ESC Alarms port.
3.13 Satellite Control Channel (SCC)
The SCC format uses a variable overhead rate to transmit an asynchronous data channel in
addition to the normal data channel. The SCC asynchronous mode implemented on the DMD50
is "PassThru" Mode.
3.13.1 SCC Framing Structure
Each SCC frame consists of the following:
A 10-bit synchronization pattern called the Synchronizing Word.
Multiple variable length slots filled with user data.
Multiple 10-bit control words that contains eight bits of in-band data (the extra two bits
are for the async start/stop).
The number of user data slots and control words per frame is selected by the SCC Control Ratio
Parameter. This can be any value from 1 to 1 through 1 to 7. A higher ratio allows a lower
overhead rate but since there are less Sync Words, there is a higher acquisition time.
The following examples show a control ratio of 1 to 3 and 1 to 1. Example 1 shows three Control
Words for every Synchronizing Word, and Example 2 shows one Control Word for every
Synchronizing Word.
TM118 – Rev. 1.1
1 to 3 Control Ratio
1 to 1 Control Ratio
Theory of Operation
3-21
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