I've not used that particular model, but in general try this.
first off, you may have the manual, but it can be downloaded at:
(download both, they're a bit different in their approaches)
if all you're trying to do is hook the EasyAIS up to your computer, i think you just need to connect the RS232
(serial) from interface box to computer serial
port. if you don't have a serial
port on your computer, use a USB to serial adapter. $10 - $20 cheap
a simpler method would be to follow the manual and wire the 2 designated wires from the RJ45 plus to a serial DB-9 plug
and don't use the interface box.
if you're using the interface box becaus it brings GPS
coordinates in, odds are they'll also be sent to your computer through the RS232.
or, like i do, hook up a USB or serial GPS
directly to the computer. OpenCPN
accepts and merges the two signals, or takes them both from one signal. settings are in Tools.
if this and the manual doesn't help, let me know. glad to advise - if i can.