What to Do if your PC has no RS232 ports

If your Windows PC doesn’t have a built-in RS232 serial port (most newer PCs do not), you can add one by purchasing an RS232 to USB adapter which typically sells for under $20.

These adapters have a USB-A connector on one end and a 9-pin male RS232 connector on the other. To use the adapter, you need to install a Windows Device Driver, which is usually provided on a CD or can be downloaded from the adapter manufacturer’s website. We recommend adapters with FTDI chipsets because they typically download the necessary driver automatically, have the most stable device driver software, and are compatible with all versions of Windows.

When you connect the adapter to your PC’s USB port, it will show up in the Windows Device Manager as a standard RS232 COM Port (typically as COM4, COM5, or another number above COM3). 

To see out the COM port number that Windows has assigned to the adapter, follow these steps:

  1. Open the Windows Device Manager.
  2. Find the section called “Ports (COM & LPT)”. If you don’t see the “Ports (COM & LPT)” section, it should appear after you connect the adapter.
  3. Connect the adapter to a USB port on your PC.
  4. In “Ports (COM & LPT),” see which port the device appears under.

If you don’t see the COM port in the Device Manager, your device driver may not be installed correctly. You may also need to be logged in as an Administrator to install the driver. Otherwise, you may need to contact the manufacturer for help.

For more information, see Identify your device’s COM Port with Device Manager.

Important notes

  • Many devices that connect to an RS232 port on a PC use a cable that has the transmit and receive lines crossed, so you may need to connect the original cable from the device to the RS232 to USB adapter. 
  • If you switch the USB port that the adapter is connected to, Windows may assign a different COM port number to it. To avoid this, we recommend keeping the adapter connected to the same USB port. If you need to change the COM port number, go to the Windows Device Manager, right-click the COM port and select “Properties.” Then, navigate to “Port Settings” > “Advanced” and change the COM port number to an available one.

Many modern RS232 devices come with a USB connection instead of an RS232 cable. These have a built-in RS232-to-USB adapter so they can still be used with standard RS232 communications software like WinWedge. As such, they won’t show up as an RS232 COM port in Windows until its device driver is installed.

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