Support Home > 5c. Determining the COM Port of a USB to Serial Adapter
There are a number of Serial-to-USB adapters that do two things:
1. They physically connect a serial cable to a USB port.
2. They have software drivers that create a Virtual COM Port.
A Virtual COM Port is a setting within the Windows Operating System that allows software products to connect to USB devices using traditional serial (COM Port) connections. While, the 'plug' on the back of the computer remains USB, the software (such as Maptech's Offshore Navigator or Terrain Navigator) connects to it as a traditional serial COM Port. It is the number of this Virtual COM Port that is needed for Maptech's software to connect to the GPS device attached in this fashion.
Setting Up Your Serial-to-USB Adapter:
Your adapter includes a CD that contains drivers for your device. A driver is a piece of software that installs into the Windows Operating System that allows all applications to communicate with the new device. Without a driver, a device can not be used.
Insert the Driver CD that accompanied your Serial-to-USB adapter and follow the instructions to set it up. If possible, verify that it is working properly through whatever means the documentation for that adaptor indicates. Unless the Serial-to-USB adapter is working properly, it will not be able to communicate with your GPS or any software application.
Determining the COM Port Number of a Virtual COM Port:
Once the driver is installed, you will need to find out the number of the Virtual COM Port that has been set up. In the majority of cases, you can determine the Virtual COM Port by following these steps:
1. Open Device Manager:
(Windows XP) Right click My Computer, and choose Manage.
(Windows Vista & Windows 7) Right click Computer, and choose Manage.
Click Device Manager on the left.
2. In the Device Manager list, look in Ports and find the Virtual COM Port, which was created by the USB driver.
i.e.___ USB to Serial Port___ (COM #).
In this example, it is COM 4:
Finishing the Job: Reading the GPS Stream in Your Maptech Navigation Application
Depending on the Maptech Navigation application you are using, the next step varies. However, the basic concept is now to "tell" it where to find the GPS Signal.
Maptech Chart Navigator Pro v1.1 (or Maptech Chart Navigator Light)
1. From the 'Tools' menu, select 'Options'.
2. Open the 'Instruments' tab.
3. Press Auto Detect.
(If the GPS signal can still not be located, use Port Settings to specify the COM port determined during the above test. Also, ensure that the Port Interface is set to NMEA and that the correct Baud Rate is selected.)
3. Once the signal is detected, OK the settings changes and press "Go To Boat" on Chart Navigator's button bar to locate the vessel.
Related Technical Document: Configuring Chart Navigator Pro (and Light) to the GPS - Basic Instructions.
Maptech Offshore Navigator (or Offshore Navigator Lite)
1. From the 'Vessel/GPS' menu, choose 'Setup', 'GPS Setup Wizard'.
2. Follow the on-screen instructions.
(If the GPS Wizard can not detect the GPS, select 'Setup', 'GPS' from the 'Vessel/GPS' menu. Set the 'Manufacturer' to 'NMEA - generic' and specify the COM port determined during the above test. Next, click Port Settings and verify the Baud Rate. Then check 'GPS on' and 'Test.')
3. Once the signal is detected, choose 'Position from GPS' from the 'Vessel/GPS' menu, then click 'Follow Vessel' in the lower left-hand corner of the chart window.
Related Technical Document: Configuring Offshore Navigator (or Offshore Nav. Lite) to the GPS - Basic Instructions.
1. Press the large "Click Here To Find GPS" button to the left of the chart window.
2. Press 'Find GPS'.
(If The CAPN can not detect the GPS, exit The CAPN, and open the GPS.INI file found in the 'C:\Capn Voyager' folder. Edit this file to include the COM port and Baud Rate determined during the above test. Save the changes and restart The CAPN)
Note: The CAPN can not use COM ports higher than 9. If your GPS is connected to COM 10 or higher, reset the drivers for that port so that a lower COM port is used.
Related Technical Document: Configuring The CAPN to the GPS - Basic Instructions.
Maptech Chart Navigator (free chart viewer)
Chart Navigator Viewer is for printing and planning with BSB nautical charts. It can not be used for plotting a position in real-time. GPS functionality is limited to the transfer of routes, waypoints, and tracks to and from handheld GPS units. To configure Chart Navigator Viewer for this purpose, choose 'Setup', 'GPS' from the 'GPS' menu.
Related Technical Document: Configuring Chart Navigator (Free Viewer) to the GPS - Basic Instructions.
Maptech Terrain Navigator (or Terrain Navigator Pro)
1. From the 'GPS' menu, choose 'GPS Setup Wizard'.
2. Follow the on-screen instructions.
(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')
3. Once the signal is detected, choose 'GPS Tracking', 'Start Tracking' from the 'GPS' menu.
Related Technical Document: Configuring Terrain Navigator (or Pro) to the GPS - Basic Instructions.
The Virtual COM Port number may change on different computers, when you install additional devices, or when you switch the USB connection to a different USB port.
Before using navigation software, the COM Port numbers created by your computer and the GPS COM port entered in the settings of your navigation software must match. Otherwise, the navigation software won’t receive the satellite signal.
If you do not see a Virtual COM Port, try to uninstall the drivers that accompanied your Serial-to-USB adapter (or USB GPS) and reinstall them. All of the Serial-to-USB manufacturers include a CD or web download to uninstall and reinstall these drivers. In practice, it sometimes takes a few tries to create a working Virtual COM port.
Several customers have reported incompatibilities with the Serial-to-USB adapter sold by Radio Shack. It appears that this adapter is unable to handle high data rates of NMEA GPS units and, therefore, we do not recommend it for use in this manner.