How many NMEA 0183 devices can the USG-1’s output drive?
Whilst the USG-1’s output is capable of driving up to 8 NMEA 0183 instruments, to maintain the galvanic isolation between each of the NMEA devices, it is recommended to connect only one NMEA device.
If all the NMEA 0183 devices connected to the NMEA output are proven to have a correct NMEA 0183 opto-isolated input, then it is possible to connect the USG-1 output to multiple NMEA devices and still maintain galvanic isolation. However, this is the only condition where multiple NMEA 0183 devices is recommended.
When connecting multiple NMEA devices, the exact number possible will depend on the total cable length, cable quality, and instrument inputs. Longer total cable lengths, poor cable resistance and capacitance, and device inputs not meeting the NMEA 0183 specifications (stipulating a maximum 2 mA drain) will reduce the maximum number of devices drivable.
If bi-directional communications are required, then only one NMEA 0183 device can be connected to the USG-1.