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NM-251A Dual-in NMEA buffer splitter 5-output (User Guide)
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Price ... 240.00 EURO
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Introduction
The NM-251A is a two channel NMEA-0183 input / four or five channels NMEA-0183 output multiplier. It enables data distribution from two NM-0183 sources (primary and secondary with priority encoding) to all NMEA-0183 instruments through four or five talker ports and PC connection through RS-232. Data from PC’s charting system can be delivered back to the autopilot from the same RS-232 port which acts bidirectional (talker and listener).
Operation
The NM-251A acquires NMEA-0183 sentences from the most significant input and immediately sends them to the general purpose outputs and the RS-232 output. A watchdog timer routine supervises if the NMEA signals are correctly applied in the primary input and switches to the secondary input whenever there is no NMEA sentence for at least eight seconds. In this case the secondary input starts receiving data if there is an instrument attached. If not, the device automatically returns to the primary input after eight seconds. When the secondary input is already in receiving mode and an NMEA signal is applied to the primary port, the device immediately switches to the primary input. In the case that no signal is applied to any input, the device “circles” around sampling the two listener ports every eight seconds until an NMEA-0183 signal appears to any of the two listener ports.
In addition the NM-251A can deliver at the same time different NMEA signals connected to Ina and Inb to output ports Out1/2 and Out3/4 respectively.
To select this function user should turn the SW-1 to ON position at the dip switch array SW1 (see figure 4) located inside the NM-251A. In this mode the user can select from which input port signals will be delivered to RS232 interface by setting SW-2 to “OFF” position for Ina or “ON” for Inb.
In addition the NM-251A can deliver at the same time different NMEA signals connected to Ina and Inb to output ports Out1/2 and Out3/4 respectively.
To select this function user should turn the SW-1 to ON position at the dip switch array SW1 (see figure 4) located inside the NM-251A. In this mode the user can select from which input port signals will be delivered to RS232 interface by setting SW-2 to “OFF” position for Ina or “ON” for Inb.
Input ports
The NM-251A has two input ports that can be connected to any instrument indented for marine use that can output NMEA-0183 signals. Each one of the two listener ports is optoisolated as specified in NMEA-0183 protocol, thus data(-) pole should never been connected to NM-251A ground. If the instrument’s talker port is single ended, connect that terminal to the Ina(+) or Inb(+) input and tide the Ina(-) or Inb(-) to instrument’s ground. If a RS-232 signal level is connected the ground pole (GND) should be connected to Ina(+) or Inb(+) and the data pole (TXD) to Ina(-) or Inb(-) respectively. The two listener ports can acquire NMEA sentences carried in TTL, RS-232 and RS-485/422 signal levels.
Output ports
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.
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.
