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OM20 Universal Outdoor Modem
The IBS Async mode MUST be selected for true Asynchronous channel
operation to be available.
4.14 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).
TM116 – Rev. 1.2
Theory of Operation
4-20
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