DMD1050 Satellite Modem Board Theory of Operation
3.17.1 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.
1 to 3 Control Ratio
1 to 1 Control Ratio
The Control Ratio of the receiving units must match the Control Ratio of the transmitting unit.
MN-DMD1050 3–29
Revision 9
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