Maintenance M7/M7L/M7LT Modular Satellite Modem
3-78 M7/M7L/M7LT - Rev. 0.05
3.6. Remote Command Interface Control
The modem command mode allows the use of an external controller or computer to monitor and
control the modem via a packet-based message protocol. This mode normally uses the RS–485
connection which allows multiple modems (and other devices) to share the command link under
control of a single or multiple entities. An RS–232 connection is also allowed but is for only a single
controller and single modem and cannot share the command link with other devices.
The packets use a unique address for each controlled device, which is set using the modem’s front
panel. The message packets themselves use a binary format for efficiency. The complete protocol is
shown in Appendix B.
The protocol consists of messages from the controller to the modem and response messages from
the modem back to the controller. The modem never initiates communications without having first
received a correctly addressed and formed message requiring a response.
Message packets to the modem can take two forms;
1. Messages requesting information in a response message or “Read”;
2. Messages commanding a change in operating parameters or “Write”.
Any write information is automatically saved to non-volatile memory
The packets of both incoming and outgoing messages take the same generic form. First are pad and
opening flag, then the destination and source addresses, followed by the command code (and read or
write mode), then necessary data. The message packet is closed with a closing flag and check word
to verify the packet integrity. The use of a source address allows multiple controllers on a single
control link.
NOTE: Special considerations are required when legacy modems are to be connected on the same
command line with the latest modes. See Appendix B for more information.
3.7. Modem Configuration
Configuring the modem operating parameters is essential before placing the unit into service. The
modem operating parameters may be set up using the front panel, the USB or the terminal command
mode. The binary remote control input may also be used if the remote interface parameters are
already known and set.
3.7.1. Configuring the Modem for Operation
The following description assumes that the modem setup is to be done manually at a depot location
or in the field via the front panel. Alternately, the modem could be automatically set up using a
controller and the command interface. No software is provided for such an external control application
and therefore this task is the responsibility of the using organization.
3.7.2. Setting Essential Parameters
The setting of several basic parameters is essential to achieve proper operation and carrier lock with
the modem. Improper setting of any of these parameters will result in failure to communicate with the
far end of the link. These basic parameters are listed here to serve as a minimum checklist for
installation. There are many other parameters, which must be set on the modem to configure
operation within a system. These include setting parameters for interface compatibility; automatic
correction for link properties; and alarm relay and display configuration. The discussion in the
following sections is to be used as a starting point and is not expected to explain every possible
configuration available in the modem.
3.7.2.1. Modulator and Demodulator
1. Carrier Frequency (Note special procedures below available for L-Band interfaces.)
2. Modulation Mode (BPSK, QPSK, 8PSK, etc.)
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