NMEA0183 is a serial data protocol first developed for marine electronics, but it has also become the standard data output of all GPS receivers and a number of other devices. Electrically it is similar to RS422, and the data is plain ASCII text, with each data packet or sentence beginning with a $, or some binary data for AIS that begins with a !.
We have designed this device specifically for NMEA data, and do basic validation of incoming data so we can discard anything that has been corrupted, so we expect each data packet to begin with a $ or a !, for example.
The downside of this is that it cannot be used for other data - we've had questions about using it as a general purpose console interface to a computer, and for using it with GPIO data, for example. So if it isn't NMEA data, it can't be used.