In Device Manager, right-click on the adapter under Multi-Port Serial Adapters and select Properties. Select the Advanced tab.
To enable the Low Latency option, select the adapter. With the adapter selected, the information pane will tell you whether or not Low latency is enabled. To change the setting, click the Properties button. Low latency may be enabled or disabled via the check box.
To change the Write Complete When Sent setting, select the appropriate port. The information pane lists the current setting for Write Complete When Sent. Click the Properties button to change the setting. Please note that this is a "per port" option, so it is enabled or disabled port by port or by checking the box "Copy these settings to all ports". If you are using the port with a printer, with a faxing application, or if you encounter other application difficulties, it is highly recommended that you enable this option.
For many applications it is often best to enable both the "Low Latency" and the "Write Complete When Sent" options.
After closing the Device Manager, wait 30-60 seconds (or longer if you have many ports) before the changes take place. Stopping and restarting the application using the ports may be required. In rare instances, rebooting the system may be required for the changes to take effect.
May 15, 2019