Input Port (listener)
The NM-251D-ZDA has one input port enabled that can be connected to any G S capable to output NMEA-
0183 signals. The input port is optoisolated as specified in the NMEA-0183 protocol, thus the data(-) pole should
never been connected to the NM-251DZDA ground. If the G S talker port is single ended, connect that terminal to the
Ina(+) and tide the Ina(-) to the instrument’s ground. If a RS-232 signal level is connected, the ground pole (GND)
should be connected to Ina(+) and the data pole (TXD) to Ina(-).
The NM-251D-ZDA input port can acquire NMEA sentences carried in TTL, RS-232 and RS-485/422 signal
levels.
utput Ports (Talkers)
Each of the four general purpose talker ports transmit the 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 the 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 then NM-251D-
ZDA (see figure 4). By shorting poles 1-2 on J6, Out5 converts the signals received from the computer to RS-422
signal level. By shorting the poles 1-3 on J6, Out5 is configured as a fifth output of the NM-251D-ZDA.
The NM-251D-ZDA 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
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