The question of interface compatibility often comes up in NMEA-0183 installations. Here is a summary of what to expect
- Almost any type of driver (TTL, RS232, RS422, etc.) will drive at least one opto-isolated NMEA-0183 listener.
- RS232 listeners (i.e. Computers) can only be reliably driven by RS232 drivers because of the negative voltage in the "idle" state. In practice, however, many RS232 receivers will interpret a 0 volt input as an "idle" (logic 1) state and thereby correctly interpret data from single-ended drivers such as TTL or older NMEA-0183 talkers.
This is why some GPS units have been successfully connected directly to a PC serial input without any signal conversion.
- RS422 drivers cannot drive RS-232 listeners because neither side of the RS422 output can be grounded to the RS232 common. Therefore, most NMEA 0183 talkers cannot be directly connected to a PC.
However, inevitably, normal operation is possible by connecting only the "A" terminal of the NMEA-0183 Talker to the RX terminal of the RS232 receiving circuit and connecting the GND of the NMEA-0183 Talker to the GND of the RS232 receiving circuit.
Once again, NMEA-0183 Talker's "B" should not be connected anywhere.
Jinbo Sim / CEO
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