User's Manual Part 2

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Signal line termination
RS422 signal lines may need termination resistors at the far end of the serial cable
connected to the NAV-7, depending on the length of connecting cable and the rate
of data transmission. Both the IBS and the NMEA ports in the NAV-7 have inbuilt
100O termination resistors for both Tx and Rx.
Whether termination is required depends on many factors, particularly the length of
the signal cable and the environment in which the equipment is operating. The
principle is shown in the sketch:
There is only one talker per twisted pair; there can be several listeners. The
intention is that terminations must be provided by the devices at the ends of the
line, regardless of whether they are listeners or the talker, and that no other device
should provide a termination.
Since the NAV-7 contains internal termination, it MUST be at the end of the line and
NOT in the middle.
It is good practice to use screened cables in all ship cable installations. Take care to
connect the cable screen to ship’s ground at one end only of the cable, as
connecting at both ends may cause ground loops and interference to the signals.
The cable screen should not be connected to any part of the NAV-7.
Connecting to the IBS serial interface
The display connection cable is supplied ready for
use, and needs only to be plugged into the
appropriate connector on the NAV-7.
Display cable: Six twisted pairs, screened, PVC
sheathed. For lengths to 200 meters, use 0.22 mm
2
(7/32); Belden 8106 or equivalent.
The connections to the15-pin socket on the NAV-7 are given below. Note that the
cable screen should not be connected to any part of the NAV-7.
Talker
(NAV-7)
Listener
(may need termination)
Ground cable
screen at
NAV-7 ONLY
Terminating
resistor