USB Serial Adapters for an Older Instrument or Peripheral
Identify the serial electrical standard and cable wiring before matching a familiar nine-pin connector.
We have not performed hands-on testing of the products discussed. Manufacturer references and official guidance support the documented information below; comparison exercises are our editorial guidance.
Older measurement equipment, label devices and control peripherals can depend on a serial connection that a current computer lacks. A USB serial adapter may bridge that gap, but serial describes a family of interfaces rather than one universal electrical arrangement. Copy the equipment's interface requirements before choosing an adapter or buying a cable based on connector appearance.
Identify the interface beyond its shell
Find the device manual's electrical standard, connector pinout and required connection type. RS-232, RS-422, RS-485 and logic-level serial descriptions require different consideration; a matching connector is not proof of interchangeability. StarTech separates serial-adapter families and publishes model-specific driver and connector information. Do not connect an unidentified adapter experimentally to valuable equipment. If the device documentation is unavailable, resolving the interface through the manufacturer or a qualified technician is the first step.
Resolve cable wiring and communication settings
Determine whether the instrument expects a straight-through cable, a null-modem arrangement or a maker-specific lead. Record connector gender, retention screws and any required handshake lines. Keep the device's baud rate and other communication settings in the same note, but do not assume an adapter automatically sets them correctly for the application. An inexpensive gender changer changes the mechanical connection; it does not necessarily correct the wiring or supply a missing handshake signal.
Check computer and application support
Find the adapter's supported operating systems, chipset information and current driver instructions for the exact model. Some older applications refer to a particular COM port, so port-assignment behavior can matter when reconnecting the adapter. On a managed work computer, establish whether the driver may be installed. Read any isolation requirement in the equipment's documentation separately; optical isolation is a specialized feature with defined limits, not a general guarantee that every installation problem disappears.
Keep the working combination identifiable
Choose a cable length that reaches the instrument without pulling on its connector, and retain the adapter model alongside the successful port and software settings. Label a device-specific lead so it is not accidentally substituted into another setup. Buy when a documented adapter-and-cable combination preserves a useful peripheral and the application can use it. Skip the adapter if the equipment already has a supported direct USB mode, or if the unsupported application and missing documentation make compatibility unresolved rather than a simple missing-port problem.
Compare the trade-offs
| Approach | Useful when | Trade-off to check |
|---|---|---|
| RS-232 adapter | The device expressly documents that electrical interface | Confirm wiring and handshake needs separately. |
| Isolated serial adapter | The installation documentation calls for defined isolation | Check the supported standard and isolation limits. |
| Native device USB connection | The equipment offers a supported alternative | Use the required driver and device mode rather than adding a conversion. |
Your purchase checklist
- Read the electrical standard and pinout in the equipment manual.
- Confirm straight-through or null-modem wiring requirements.
- Check operating-system and application support.
- Verify driver installation permission when relevant.
- Label the complete successful device-specific connection.
Sources and further reading
- USB Serial Adapters - RS232 | DB9 | RJ45 | StarTech.com Europe
- USB to Serial Cable | COM Retention | For Servers/Printers/Barcode Readers/AV | Prolific Chipset |Windows/Mac/Linux
Reference links concern the stated topic or example. They do not indicate endorsement of this publication. Product versions, local labels, availability and seller terms can change; verify the exact listing before ordering.