Note: The DST800 can be NMEA0183, NMEA2000, or Analog.
If it's part of a Raymarine ST70 System pack it's likely analog. Best thing to do is get a photo
of the wire end posted, along with the SKU or part# you actually ordered/purchased so we know what the signalling version actually is for the unit you have.
If it's analog, you need to use a Raymarine ITC-5 along with a SeaTalkNG<->DeviceNet adapter cable to put it on a normal NMEA2000 network.
If it's NMEA2000, you just need the SeaTalkNG<->DeviceNet adapter cable
If it's NMEA0183, (which is unlikely if it was for a Raymarine system, then you need an NMEA0183 to NMEA2000 converter, or possibly just hardwire to a chartplotter
But just saying DST800 is not enough to know which of the 3 modes it's built for.