nuova marea ltd
marine electronics & design
Address: 26 Mirtidiotissis str, Kastella, 18533 Piraeus, Greece
Tel.: +30.210.4134628, +30.210.4134698, Fax: +30.210.4134814
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Output Ports (Talkers)
Each of the four general purpose talker ports produce NMEA sentences in both RS422 and TTL signal
levels, depending on the connection topology chosen (see figure 1, 2 and 3), and can fan out one instrument.
Current drawn from every port can be up to 20mA, efficient enough to drive any NMEA compatible instrument.
The RS-232 port can deliver NMEA sentences to any modern computer running the appropriate software
on Windows 98 and above provided that serial communication follows the 4.800/8/N/1. This port is not optically
isolated and should be used for testing purposes only to avoid DC leakage. It can be used though to interface a
computer system if proper isolation is achieved or if the computer is supplied from an isolated power supply.
The Out5 port has two functionality modes that can be selected via jumper J6 located inside NM-251A
(see figure 4). By shorting poles 1-2 on J6, Out5 converts signals received from computer to RS-422 signal
level. This functionality is independent from the rest of the NM-251A circuits and is intended to be used for
interfacing Electronic Charting Systems (ECS) with autopilot systems. By shorting poles 1-3 on J6, Out5 is
configured as a fifth output of the NM-251A. Further details on how to configure the functions of the NM-251A
are shown on table 1.
The NM-251A can be connected as shown in figures 1,2 and 3 using all RS-422 outputs (figure 1), all
TTL outputs (figure 2) or using either the RS-422 or TTL output of each port taking care not to connect the
same port for both signal level outputting.
Figure 1: Connection to RS-422 Outputs
