Radyne OM20 Specifications download pdf (Page 60)

OM20 Universal Outdoor Modem OM20 Theory of Operation

MN-OM20– Revision 5 4–22

4.15.1 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.

4.16 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 DMD20

is "PassThru" 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 involved. The maximum in band rate supported is 115200bps.

The Asynchronous Data Interface (J17) is a 9-Pin Female “D” Connector. The data interface is

either RS232 or RS485 via a front panel selection. Refer to Table 5-7 for pinouts.

4.16.1 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.

Figure 4-10. 1 to 3 Control Ratio diagram

1 2 ... 55 56 57 58 59 60 61 62 63 64 65 ... 219 220

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Radyne OM20 Specifications Page 60