Nera Inmarsat-c Service Manual page 19

1.3 Connection
1) Connecting the distress alert received unit and ALAM unit
The distress alert received unit: IC-305 and up to 3 ALARM units: IC-306 are
connected to port #1 to #4 in parallel. The electrical rating of port #3 and #4
(TD/RD-A/B) connecting line is RS-485. Each unit needs to be set for identification
such as DIS, RCV-1, 2 and 3. And IC-305 and IC-306 are controlled by the setting of
"Command Window" in [F8]-2: system menu. Terminal unit communicated to these
units recognizes each unit by this setting.
2) Connecting NAV data (IEC-61162)
Ports #6 and #7 (TD-A/B) are used for transmitting NAV data. To transmit NAV data,
optional GPS receiving board (GN-79) is needed.
Ports #8 and #9 (RD-A/B) are used for receiving NAV data. The external GPS data
needs to be connected.
3) Connecting DMC-5
Ports #11 to #15 are DMC-5 connecting terminals. The electrical rating is C. Loop.
DMC-5 is controlled by the setting of "Command Window" in [F8]-2: system menu.
Note) RS-485
This is like RS-422 (balanced). It is half-duplex, and not just point-to-point but like
Ethernet since all devices (nodes) on it share the same "bus". The driver output signal
level (loaded minimum) is +/-1.5 V.
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