Asynchronous Multiplexer Mode; Esc Backward Alarms; To Disable The Esc Backward Alarms; Satellite Control Channel (Scc) - Radyne DMD20 Installation And Operation Manual

DMD20/20LBST Universal Satellite Modem

3.12 Asynchronous Multiplexer Mode

Since many of the frame bits in the standard IBS mode are not used, an "Enhanced" Multiplexer
Mode has been implemented that can be engaged under software control. Since this mode
changes the use of many of the framed non-data bits, this mode is only usable when the modem
is at both ends of a link.
In this mode, the overhead signaling bytes 16 and 48 can be used to implement a significantly
higher speed ES to ES Data Channel under software control. This rate is 16 times that of the
normal IBS standard, or 1/30
The IBS Async mode MUST be selected for true Asynchronous channel
operation to be available.
IMPORTANT

3.13 ESC Backward Alarms

When running in IDR Mode and if the modem has the ESC Option, there will be four Backward
Alarms available for use by the earth stations at each end of the link (both ends must have the
ESC option). These alarms are accessed via the ESC ALARMS Port. The four alarms are
controlled by four relays, each having a normally open, normally closed, and a common
connection. The common connections of these relays (referred to as Backward Alarm Inputs)
can be connected to whichever system on the earth station that the user wishes to trigger the
backward alarm.
When ground is applied to the Common (Input) Connection of one of these relays, that relay and
associated backward alarm will then be in a "no fault" state. When the ground is removed, the
relay and the associated Tx Backward Alarm will toggle to the faulted state. When in the faulted
state, the receive end of the link will receive that backward alarm that is initiated at the transmit
end of the link.
The user can connect whichever systems on the earth stations that they desire to these
Backward Alarms Relays as long as they will supply ground to the Backward Alarm Relay Input in
the "no fault" condition and the ground will be removed in the "faulted" condition.
For example: the user could connect the Demod Summary Fault of the modem to the Backward
Alarm 1 Input, so that if the demod went into Major Alarm (such as a Carrier Loss), Backward
Alarm 1 would be transmitted to the receive end of the link. At the receive end, it would show up
as Rx Backward 1 (Receive Backward Alarm 1).
3.13.1

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.

3.14 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.
MN-DMD20-20LBST Revision 14
th
of the terrestrial data rate (1/32
Theory of Operation
nd
of the aggregate rate).
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