NMEA 0183 (RS-485)¶
RS-485 is the standard electrical interface for NMEA 0183 communication in marine environments. HALSER provides separate RS-485 receive and transmit interfaces for bidirectional NMEA 0183 communication.
RS-485 RX — Receiving NMEA 0183 Data¶
The RS-485 RX interface is the primary input for receiving NMEA 0183 sentences from marine instruments.
Wiring¶
Connect the instrument's NMEA 0183 output to the RS-485 RX 3-pin terminal block:
| Pin | Signal | Description |
|---|---|---|
| 1 | GND | Signal ground |
| 2 | A | Non-inverting signal |
| 3 | B | Inverting signal |
A/B labeling
Typically, A is the non-inverting (+) signal and B is the inverting (−) signal. However, some devices and standards use the opposite convention. If communication doesn't work, try swapping A and B — reversing the polarity is safe and will not damage either device.
Bit Rate¶
The standard NMEA 0183 bit rate is 4800 bit/s. Some devices use higher rates:
| Bit Rate | Typical Devices |
|---|---|
| 4800 | Standard NMEA 0183 instruments (wind, depth, heading) |
| 38400 | AIS transponders, high-speed GPS receivers |
The bit rate is configured in firmware. The default firmware uses 4800 bit/s and provides a web UI setting to change it.
RS-485 TX — Sending NMEA 0183 Data¶
The RS-485 TX interface sends data to NMEA 0183 listeners such as chart plotters, autopilots, or displays.
Wiring¶
Connect the RS-485 TX 3-pin terminal block to the listener's NMEA 0183 input:
| Pin | Signal | Description |
|---|---|---|
| 1 | GND | Signal ground |
| 2 | A | Non-inverting signal |
| 3 | B | Inverting signal |
Compatible Devices¶
HALSER's RS-485 interfaces work with most NMEA 0183 instruments, including:
- Wind instruments (outputting MWV sentences)
- GPS receivers (outputting GGA, RMC, VTG)
- Depth sounders (outputting DPT, DBT)
- Heading sensors and compasses (outputting HDG, HDT)
- Speed sensors (outputting VHW)
- AIS transponders (outputting VDM, VDO — RS-422 is electrically compatible with RS-485)