USB-C to Serial Adapter

Starting in High Sierra 10.13, macOS enforces stricter security policies than previous revisions. As a result of these changes, software packages, like those used in this installation, will need to be allowed within the macOS Security and Privacy settings, immediately after the software has been installed, in order for the device to operate.

To allow the software, follow these steps after you've completed installation on your Mac:

1. Open System Preferences.
2. Open Security & Privacy.
3. Click the Allow button near the bottom of the General tab.

Note: The option to allow the software will be available within the Security & Privacy settings for 30 minutes. If the software is not allowed within that time frame, the software must be reinstalled in order for macOS to grant the opportunity to allow it again.

Older applications that use serial communication often use legacy hardware addresses that do not work with PCI, PCIe, or USB to Serial products. We recommend contacting the software provider/support team to check if this is the case.

When you troubleshoot issues with a serial device, there are some quick tests that you can complete to rule out potential problems. You can test to make sure that the following components are working correctly and are not the source of the issue:

• Serial cables

• Serial ports

• Serial devices

To test your setup components, try the following:

• Use the serial cable, serial port, and serial device in another setup to see if the problem is with the components or the setup.

• Use a different serial cable, serial port, and serial device in your setup to see if the problem persists. Ideally, you should test a component that you know works in another setup.

When you test your cables, it is recommended that you do the following:

• Test each cable individually.

• Use short cables when you are testing.

When you test the serial ports and serial device, it is recommended that you do the following:

• Press the Windows key + R, type devmgmt.msc, and press Enter to open Device Manager. Check to see if your device is listed under Ports (COM & LPT).

• Make sure that the COM port number is the correct number for the serial device and that the software being used to connect the computer to the serial device uses the correct COM port number. 

• If the device is listed with an error, follow the instructions on the website to reinstall the drivers.

Note: Some serial devices work only if the COM port number is between a certain range. For example, COM1 to COM4.

• Perform a serial loopback test.  See this FAQ on how to perform a RS-232 serial loopback test: http://www.startech.com/faq/serial_loopback_test_rs232_windows

To check whether or not an RS-232 serial port is working, perform an RS-232 loopback test by doing the following:

1. If your serial port is not female, convert it by taking a female/female cable or gender changer and plugging it into the serial port.
2. Take a metal paperclip or wire and cross pins 2 and 3. If you look closely at the female end, the pins should be numbered.
3. Open a telnet session on the COM port number of the device that you are testing. To find out the COM port number, refer to the following FAQ: https://www.startech.com/faq/com-port-listing-windows.

Note: To open a telnet session on the COM port, you need a telnet client like PuTTY or Hyper Terminal. Windows XP comes with Hyper Terminal.

4. When the session is open, anything you type into it you should see. The loopback test fails when you cannot see what you are typing.

If the loopback test fails, make sure that the serial cable or gender changer that you are using works and that the adapter is in the correct port. 

You can check multiple ports at the same time by opening multiple sessions, putting the loopback adapter on one port, and trying to type into each session.  When you can see what you are typing, you know that the COM port is working and you can see which port number the physical serial port is. Close the window for the port that you just tested to speed up the testing of the remaining serial ports.

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Use a USB to Serial product that features COM Port Retention.  These products will store settings that are unique to the connected device in non-volatile memory, allowing you to retain the desired settings regardless of the USB Port to which the adapter is connected.