Comtech EF Data DMD1050TS, Инструкция по установке и эксплуатации

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DMD1050TS Satellite Modem Board
Revision 1
Theory of Operation 3–32 MN-DMD1050TS
3.17 Satellite Control Channel (SCC) – J3
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 DMD20
is Pass Thru Mode.
In Pass Thru Mode, there is no formatting or deformatting of the input data in the buffer, and it is
transmitted on a first-in first-out basis. In-band data entering the remote port is inserted into the
user data stream. The in-band data is received and passed on to the user without any
deformatting or depacketizing. The maximum in-band rate supported is 115200 bps.
The Asynchronous Data Interface (J3) is a 10-pin Dual Row header. The data interface can be
configured for RS232 or RS485 via the Web Browser or Terminal Screen.
3.17.1 SCC Framing Structure
Each SCC frame consists of:
•
A 10-bit synchronization pattern called the Synchronizing Word
•
Multiple variable length slots filled with user data
•
Multiple 10-bit control words that contain 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 because there are less Sync Words, there is a higher acquisition time.
These examples show control ratios 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.
Example 1: 1 to 3 Control Ratio