I don't know what COM Port my GPS is connected to. What should I do?

Electronics Hookup and Configuration

There are 4 types of connections between a GPS and the computer:


1. Standard Serial Connection
For a Standard Serial Connection, the GPS is transmitting NMEA data at 4800 over a serial cable. This cable is connected to a "DB9" connector on the back of the PC - which looks like a "D" with 9 pins (or sockets.) This is the most common installation on "desktop" style PCs and older GPS units.

2. Serial GPS connected to a USB-to-Serial adapter
In this connection, the Serial Connection (DB9 - described above) from the GPS is mated with a USB-to-Serial adapter that converts the signal into a USB connection. The USB connection is flat and commonly used to interface with mice, printers, digital cameras, and many other computer accessories. Since most laptops lack standard serial connections, this is the most popular option for navigators using a laptop and older GPSs.

3. USB GPS antenna only connected directly to the PC
Growing in popularity are USB GPS antenna units. These are often the size of a PC mouse (or smaller) and feature a USB cable that connects directly into the computer. There are many popular models - an Internet search of "GPS Mouse" will yield many choices.

4. Garmin Handheld GPS connected to the PC
Garmin offers a line of handheld GPS units (such as the GPSMap 60, or Oregon 550) that connect to the computer via the USB Port. These interface to the PC in a fashion unlike the other three connection types listed above. As such, they are not the subject of this knowledge base article. Instead, please refer to Connecting a Garmin USB GPS.

With the exception of handheld Garmin GPS units that connect via USB, Terrain Navigator Prointerfaces with the GPS through the use of a "COM Port". This may be a physical connector on the back of the PC, or a virtual connection provided through a software driver.

I have a Standard Serial Connection. How do I determine the COM Port the GPS is connected to?
The easiest way to determine the COM port is to use MTTTY to verify that a NMEA data stream is being received by the computer from the GPS. To do this, set the GPS in NMEA interface mode (most GPSs are always in NMEA Interface mode, only those offered by Garmin may have other modes.) Then, refer to: Using MTTTY to test and verify the GPS connection

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator to connect to the GPS.

I have a Serial GPS connected to a USB-to-Serial adapter. How do I determine the COM Port the GPS is connected to?
All USB-to-Serial adapters require software drivers to operate. Thus, a software driver CD-ROM accompanied your adapter. If the CD was missing or has been lost, download the driver from the manufacturer's web site. Once the driver has been installed, click here to determine the virtual COM Port of a USB to Serial Adapter.

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator to connect to the GPS.

I have a USB GPS antenna only connected directly to the PC. How do I determine the COM Port the GPS is connected to?
All USB GPS antennas require software drivers to operate. Thus, a software driver CD-ROM accompanied your GPS. If the CD was missing or has been lost, download the driver from the manufacturer's web site. Once the driver has been installed, it functions identically to a GPS connected through a USB-to-Serial adapter; click here to determine the number of this type of virtual COM Port.

An exception to this is the (now discontinued) Garmin 18 USB GPS. For it to function properly with Terrain Navigator Pro, it must be configured as a NMEA GPS. This is done through a product known as "Spanner." To download the latest version of Spanner, please visit this link to Garmin's web site.

Once you have determined the COM Port, enter this value into the GPS Setup screen of Terrain Navigator Pro to connect to the GPS.

Finishing the Job: Reading the GPS Stream in Terrain Navigator Pro

  1. From the 'GPS' menu, choose 'GPS Setup Wizard'. 
  2. Follow the on-screen instructions.
  3. If the GPS Wizard can not detect the GPS, select 'Setup' from the 'GPS' menu. Set the 'Manufacturer' to 'NMEA - generic' and specify the COM port determined during the above test. Also, ensure that the correct baud rate of the GPS is selected in Port Settings. Then press 'Close'.
  4. Once the signal is detected, choose 'GPS Tracking', 'Start Tracking' from the 'GPS' menu.

Related Knowledge Base Article:
Configuring Terrain Navigator Pro to the GPS - Basic Instructions.

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