Introduction

The NM-251D-CS is a member of the NM-
251 Series family and is programmed to function
as a NMEA-0183 Checksum tracker/calculator.

Operation

The NM-251D-CS acquires the NMEA-0183 strings from the Ina port provided that they follow the 4.800/8/n/1 serial format. The NM-251D-CS will automatically detect if the input string is stripped from the checksum characters, it will calculate and append the checksum to the output string. The new NMEA-0183 string is then transmitted to all five RS-422 output ports and the RS-232.
Input Ports (listeners)

The NM-251D-CS uses one of the two input ports. The input port Inb is not available at the NM-251D-CS custom interface and should not be connected. The listener port Ina is optically isolated as specified in NMEA-0183 protocol, thus data(-) pole should never been connected to NM-251D-CS ground. If the instrument’s talker port is single ended, connect that terminal to the Ina(+) input and tide the Ina(-) to instrument’s ground. If an RS-232 level signal is connected, the ground pole (GND) should be connected to Ina(+) and the data pole (TXD) to Ina(-) respectively. The listener port Ina can acquire NMEA sentences carried in TTL, RS-232 and RS-485/422 signal levels.

Output Ports (Talkers)

Each of the four general purpose talker ports can output 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 all port can be up to 40mA (maximum rating 60mA @ 24VDC power supply) simultaneously, efficient enough to drive any NMEA compatible instrument.

Installation & Operation manual