M7/M7L/M7LT Modular Satellite Modem Operation
M7/M7L/M7LT - Rev. 0.05 1-21
The “4-Wire” setting forces the driver continuously on while the “2-Wire” setting controls the output
into tri-state when the modem is not transmitting data, allowing multiple modem outputs to be
connected together. In the standard IBS mode only the “4-Wire” mode is available.
In Custom or Advanced mode a 2 wire receive operating mode can be selected for the receive data
into the ESC channel. In this mode the receive input is muted while the transmit data output is active.
In 4 wire mode the receive input is always enabled. In the standard IBS mode only the 4 wire mode is
available.
NOTE: Transmit and receive pairs are physically separate wires and must be connected together if
true RS-485 2 wire connectivity is desired.
The ESC Async Mode can be selected to Auto or Manual modes. In the Auto mode, the <Intf: Send –
Mux Overhead Ratio> is calculated based on the <Intf: ESC – Async Rate>. When the <Intf: ESC –
Async Mode> = Manual Overhead Rate, the <Intf: Send – Mux Overhead Ratio> is calculated based
on the <Intf: ESC – Async Rate> and the <Intf: Send – Mux ESC Rate>. The recommendation is to
use the Auto mode unless the operator is an expert user.
The user does not have to compute data framing variables to use the Custom or Advanced
Multiplexer Mode. When placed in this mode the entry parameters are the ESC and MCC channel
rates selected from standard asynchronous data rates (300bps to 3.5Mbps). The modem then
computes the proper relationship between the framing and terrestrial data rates to achieve the proper
operation. The modem also displays the terrestrial data to aggregate ratio.
NOTE: The Auxiliary Overhead Channel Multiplexer/Demultiplexer function is available in all of the
synchronous baseband interface option. This would include the Multi-Sync, Dual G.703, and
HSSI interfaces.
NOTE: The Advanced mode is only available when the FEC is set to TPC or LDPC.
1.5.8. Modem Control Channel (MCC)
In the synchronous baseband interface options, the MCC is available in both the Custom and
Advanced Multiplexer modes. In these modes the MCC provides for the AUPC plus the Remote
Modem Control (RMC) Channel and the Auxiliary control bits (RFC).
In the Ethernet and IP baseband interface options, the MCC channel is provided without the need to
setting a separate multiplexer or demultiplexer function.
1.5.9. AUPC Control Channel (AUPC)
When the modem is placed into either the Custom or Advanced modes, the AUPC control channel
becomes available. The AUPC operation itself is under control of the modem while the AUPC facility
in the MCC provides the channel for the information. This channel provides a minimum 300 baud
control channel in each direction to allow the modems at two ends of a link to interactively maintain
the receive Eb/No by controlling the power output at the transmit site.
Refer also to the AUPC operation description of the main manual in Section 3.10.
1.5.10. Auxiliary Bit Control Channels (RFC)
When the multiplexer is placed into the Custom or Advanced mode the auxiliary bit control RFC
channels becomes available. In the IESS standards, these are commonly referred to as “Backward
Alarms”. These consist of two single line or “one-bit” control channels that can be used to send
control information independently in both directions over the link. The input signals on these channels
can be either a contact closure or a logic type signals while the output is a form C relay contract set
whose state depends on the state of the input signal. The low input logic level is 0 to 0.4 VDC, while
the logic high level can be from 2.4 to approximately 20 VDC. The input is current limited to accept
this wide voltage range without damage. Higher voltages may damage the inputs however and
caution should be exercised. Pin connections for these one bit channels are shown in the connector
pinout of each interface in Section 0.
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