How to Set Up a USB to Serial Adapter for Legacy Devices
By Plugable #1 in Docking Stations and USB Devices ~ Plugable ... | Published: 2026-10-20
Category: How-to Guides
Connect legacy RS-232 devices to a modern computer with a USB to DB9 adapter. Learn the setup steps, driver notes, and COM port checks for a reliable connection.
Quick answer
To connect a legacy RS-232 device to a modern computer, plug a USB to serial adapter into a USB port, install the matching driver, then set the correct COM port and baud rate in your software before testing the link.
Why the chipset matters for serial adapter setup
The chipset inside a USB to RS-232 adapter determines which operating systems it works with and how stable the connection stays. A Prolific PL-2303GT chipset is a common choice because it combines solid performance with wide driver support. That matters when you connect barcode scanners, CNC controllers, or industrial sensors that expect a real COM port rather than a USB connection.
Most modern Windows versions recognize Prolific-based adapters without extra setup. Windows 7 through 11 include native driver support, so the adapter usually appears as a COM port as soon as you plug it in. macOS and Linux users still need the matching driver, and the open-source driver included in the Linux kernel covers most distributions from kernel 2.4.31 onward.
The trade-off to keep in mind: not every legacy device uses the same serial settings. Even a correctly installed adapter will not communicate until you match baud rate, data bits, parity, and stop bits with the device you are connecting. The adapter handles the USB side; the software side is where most setup errors happen.
How to set up your USB to serial adapter
- Install the driver first: On Windows 7 through 11, the Prolific PL2303GT chipset uses native drivers, so no installation is needed. For other operating systems, download the driver for your OS version before connecting the adapter to avoid a failed enumeration. Check Device Manager for a COM port entry before plugging in your device.
- Plug in the adapter and note the COM port: Connect the USB end to your computer and the DB9 end to the legacy device. Open Device Manager (Windows) or System Information (macOS) and locate the adapter's COM port number, such as COM3 or COM5. Write down the COM port number; you will need it in the software that talks to the device.
- Install or confirm the driver: On Windows 7 through 11, native driver support means no installation is needed. For other systems, install the Prolific PL2303GT driver package. If the device shows a warning icon, update the driver manually or reinstall the package from the vendor site. Confirm the adapter appears under Ports in Device Manager before moving on.
- Set the COM port and baud rate: Open Device Manager, expand Ports, right-click the adapter, choose Properties, then Port Settings. Match the baud rate, data bits, parity, and stop bits to the legacy device's manual, and note the assigned COM number for your software. If the COM number is above 9, change it to a lower number in Advanced Port Settings to avoid older software refusing it.
- Test the connection: Use a terminal program (PuTTY, Tera Term, or the vendor utility) to send a test command to the device. Confirm the device responds at the configured baud rate before starting your real application. A loopback test with a shorted pin can confirm the adapter is transmitting and receiving before you connect the legacy device.
Why the chipset matters
- Plugable USB to RS-232 DB9 Serial Adapter (Prolific PL2303GT Chipset): The Plugable USB to RS-232 DB9 Serial Adapter uses the Prolific PL-2303GT chipset and includes drivers for Windows 11 through Windows 7, Windows Server 2008-2022, macOS 10.6 and later, plus open-source drivers in the Linux kernel 2.4.31 and later. Broad driver coverage means the adapter can connect to nearly any modern desktop or laptop without hunting for a rare legacy driver.
Plugable USB to RS-232 DB9 Serial Adapter (Prolific PL2303GT Chipset) - Plugable USB to RS-232 DB9 Serial Adapter (Prolific PL2303GT Chipset): Windows 7 through 11 offers native driver support, so no separate installation is needed on those systems. On current Windows versions you can plug in and start working immediately, which removes the most common setup failure point.
