Serial Ports on the back of a computer tower are assigned logical identifiers, referred to as COM ports within Windows Operating Systems. COM ports are used to communicate with external devices attached to the port through the RS-232 communication standard. Physical serial ports on the back of a computer are generally assigned to COM 1 or COM 2 as shown below.
If you only have one Serial Port on the back of your computer it can safely be assumed that this port has been designated as COM 1. Determining which serial port is assigned to a specific COM port is best done through trial and error. The Device Manager Utility within Windows can be used to determine what COM ports are in use on your system.
Device Manager
Device Manager is a utility included with Microsoft Windows Operating systems, which allows users to display and control hardware items attached to a computer.
Opening Device Manager:
Click Start
Click Run
Type devmgmt.msc into the Run Dialog Box as shown below.
Click OK. Device Manager will be displayed.
Click on the Plus sign to the left of Ports (COM & LPT)
A list of assigned COM ports will be displayed.
COM1 is associated with one of the Serial Ports on the back of the computer as introduced in the beginning of this document. COM 2 is associated with the other Serial Port on the back of the computer, assuming there are two. COM 3 is associated with a USB to Serial Adapter as explained later in this document. Knowing which COM ports are installed on your computer can help you to determine which port to assign in the InfiniTime software when configuring your clock.
If multiple COM ports are installed on your computer and you have more than one serial port on the back of your computer’s tower then a trial and error approach, as outlined below, must be used to determine which COM port your direct connect clock is connected to.