The RS-485 communication protocol is a bus protocol, that is, devices can both send and receive on the same two wires.
The RS-232 communication protocol is a point-to-point, one way communication, TALKER to LISTENER.
NMEA-0183 began with RS-232 as the communication protocol but evolved to RS-422. R-422 is similar to RS-232 but uses balanced signals. This is why I recommended you set up the device you want to communicate with NMEA-0183 as an RS-232 output. RS-232 output can be easily interfaced to a newer RS-422 input.
Whether RS-485 can be directly connected to NMEA-0183 is unknown to me.
When the device says it has "Data Format NMEA-0183" the device is talking about how the data is formatted, that is, it will use NMEA-0183 data structures like the sentence name MWV and the content of the MWV sentence. But it sends this data using the electrical characteristics of a data communication standard called RS-485 also sometimes called MOBUS. Using of NMEA-0183 sentences is very common, as the protocol is old (c.1983) and many products use it to format the data they want to send to other devices. It is a common language.
In real NMEA-0183 connections, the electrical characteristics of the data communication is either RS-232 of RS-422. These are specifications for the electrical nature of the signals, not for how the data is to be formatted.
The other electrical data communication specification mentioned by the device is "UART/TTL". If you can configure the UART to operate in RS-232 or in RS-422 model, then you will be able to interconnect to a NMEA-0183 LISTENER. If the UART only works at TTL voltages, it may not work with an NMEA-0183 LISTENER.
An interesting comment about connecting an RS-422 receiver (or in other words a NMEA-0183 LISTENER) to an RS-485 bus (in other words, the device you have) can be found at:
https://www.edaboard.com/threads/compat ... -422.8051/In that thread a contributor mentions:
RS422 is a one way bus: one transmitter and multiple receivers on the bus.
RS485 is two way: multiple transceivers on the bus.
Both busses use two-wire differential signals with identical voltage levels.
From a hardware point of view it is possible to connect RS422 receivers to an RS485 bus. You cannot place an RS422 transmitter on an RS485 bus. In other words: with a RS422 receiver you can only listen to an RS485 bus.
RS485 is only the hardware standard and says nothing about transmission protocol, so keep that in mind.
To me, this seems to suggest that connecting your device's RS-485 output to a NMEA-0183 differential LISTENER should work. It should allow the NMEA-0183 device to see the RS-485 output; and if that output is in the NMEA-0183 data format, it should work.
If you don't get this outcome, check the baud rate configuration. There are only two baud rates in NMEA-0183: 4800 is standard and 38,400 is "high speed."