Multiple COM Port Inputs on Windows Laptop?

I run Coastal Explorer on a Windows laptop. It receives GPS and AIS data via NMEA 0183 from a Standard Horizon VHF through an NMEA multiplexer via USB (COM 3). The multiplexer also supplies vessel heading from a KVH Azimuth electronic compass, and sends steering instructions to the autopilot.

My Garmin Striker depth finder doesn’t offer NMEA 0183 data, but rather sends data in the Garmin proprietary format to other Garmin devices.

Question: Since Coastal Explorer can read the Garmin binary protocol, can I provide depth information from the Garmin via a serial (RS232) USB connection through a second COM port on the laptop?

Thanks in advance!

Follow up: I have connected a FTDI serial USB device to the Garmin Striker. It is easily recognized as “online” by CE on COM4, Garmin selected on the pulldown, but it returns the error: “COM Port Problem: Receive Framing Error (Incorrect BAUD Rate Selected?)” Garmin says that they use NMEA 0183 at 4800 or 38,400 BAUD, but CE’s auto-detect is unable to lock onto anything.

Per guidance from Garmin, I have the Striker blue wire (Tx) connected to the interface’s yellow (Rx) and the Striker’s brown (Rx) to the interface’s orange (Tx). The interface’s black (gnd) is wired to the common DC negative bus that the Striker is on.

Many Garmin products support both Garmin’s proprietary protocol at 9600bps as well as NMEA 0183 at 4,800bps. In reading Garmin’s manual could not decipher whether the Stryker does both but suggest confirming and configuring both sides to use the same protocol.

Our support for the Garmin protocol hasn’t changed in the 15 years I’ve been here, so it may not always work as expected. We added support during a time when Garmin published this protocol. They have since removed the documentation so we cannot keep it up-to-date. I doubt very much that our support even worked with depth, but I’m not 100% sure. If it’s not working, though… We recommending using NMEA 0183. This is preferable for many reasons, such as it being a non-proprietary standard and it being much easier to troubleshoot since it’s not binary. Is your Garmin fish-finder connected to a chart plotter? Perhaps it had act as a relay for sending NMEA 0183 or NMEA 2000 depth sentences/pgs?

Thanks for your response. I did find much more detail from Garmin in their “device interface SDK” paper, found at With so much conflicting information on various official Garmin sites, it would seem that this is actually the final word on their “NMEA” interface. I put it in quotes because they use proprietary sentences over a non-standard serial interface. I tried many different permutations, but finally gave up on getting the Garmin to talk to CE.

I know that I’m not the only one to express frustration at the use of proprietary interface protocols among marine electronics manufacturers.