A USB to serial cable will link a new computer that does not have an integrated serial port with an older device that relies on one. The chipset in the cable translates the USB signal into serial signal of the target device: RS232, RS485, RS422, TTL UART or a console interface over RJ45.

Such cables are commonly applied in industrial automation, network device control, embedded development and IT support. The correct cable will be based on the serial interface of your target device.

What Types of USB to Serial Cables Are There?

There are 5 major types. They all focus on various serial standards and application groups.

USB to RS232 Cable

RS232 is the most popular legacy serial system. It works on the basis of single-ended signaling where two devices can be connected through point-to-point communication and has a functional length of about 15 meters.

Most serial ends will use a DB9 connector (9-pin), or an older version of equipment will use a DB25 connector (25-pin). RS232 ports can be found on PLCs, POS terminals, lab instruments, industrial controllers and old computers.

Common applications:

• PLC programming and diagnostics
• Barcode scanner and POS terminal connection
• Laboratory and measurement instrument configuration
• Legacy industrial controller access

Prior to purchasing: Check what kind of port the device has, i.e. male or female, and whether you require a straight-through or null-modem (crossover) cable. They are not interchangeable.

USB to RS485 Cable

Differential signaling of RS485 is used in a two-wire (A/B) bus. It has high noise immunity, allows cables runs up to about 1200 meters, and can accommodate more than two devices on one bus, i.e. up to 32 nodes in standard implementations.

RS485 is the physical layer of Modbus RTU, which is the most popular protocol in industrial automation. It is also applied in BACnet MS/TP, DALI and energy metering systems.

Common applications:

• Modbus RTU communication with PLCs, VFDs and sensors
• Building automation and HVAC systems
• Energy meter and sub-metering networks
• SCADA data collection

Most important point: Most RS485 systems are half-duplex: the data flows in the opposite directions each time. The converter needs to be able to switch directions of transmission/reception. Make sure this is done automatically (auto-direction control) before implementing it into operational Modbus network.

USB to RS422 Cable

RS422 is an RS485-type differential standard but it is intended to work as full-duplex with dedicated transmit and receive pairs, i.e., four wires instead of two. It can be used over long cable lengths and allows a single transmitter to drive several receivers.

RS422 is found in industrial control systems, motion control interfaces and specialized equipment when full-duplex differential communication is needed. Most of the USB to RS485 converters are compatible with RS422 mode as well — refer to the wiring diagram to make sure that the four-wire setup is used.

USB to RJ45 Console Cable

Administration of managed routers, switches, firewalls and other similar network devices consists of a console port, which is usually an RJ45 socket, to provide direct local administration. The port does not connect to the device Ethernet interfaces but transmits serial signals.

USB to RJ45 console cable allows engineers to access the device CLI directly through a laptop in order to configure, recover the firmware or troubleshoot the device when IP access is not available.

Note that an RJ45 console cable and an Ethernet cable have the same connector, but they have a different electrical property. One transmits serial data whereas the other transmits network data. They cannot be used interchangeably.

Also remember that console port pinouts differ across manufacturers. Make sure that it is compatible with the particular device you have.

Other devices such as some UPS systems and outdated networking equipment are designed with a 6-pin RJ11/RJ12 (6P6C or 6P4C) management slot in lieu of an RJ45 socket. They also require the appropriate cable versions.

USB to TTL UART Cable

The TTL UART cables can transform USB into logical level serial signals that are required by the microcontroller and development boards. They are common devices in firmware debugging, bootloader access, and serial console connection to single-board computers.

The voltage level is important. There are also three voltages of TTL UART cables: 3.3V and 5V. A 5V cable may cause damage to a 3.3V device. You should always check what logic level your device needs prior to operation.

The serial end usually adopts Dupont wires or 2.54 mm pin headers. The common pins are GND, TX and RX along with some other cables that have VCC and flow control pins. The TX cable connection should be placed on RX of the device and vise versa.

Common applications:

• Microcontroller and MCU firmware debugging
• ESP8266 / ESP32 / Arduino serial communication
• Raspberry Pi and SBC serial console access
• IoT device bootloader and firmware flashing

USB-C to Serial Cables

All the types above have USB-C variants. The conversion is similar but the connector on the host side changes. In case your laptop has only USB-C ports, they remove the necessity of using extra adapters.

Comparison: RS232, RS485, RS422 and TTL UART

Do USB to Serial Cables Need Drivers?

Yes, in most cases. The cable's internal chipset needs a driver to create a virtual COM port on the host computer. Four chipsets account for most of the market:

For individual use, driver installation is straightforward. For deploying across multiple machines or production environments, verify driver availability for your specific OS version before selecting a cable.

How to Choose the Right USB to Serial Cable

1. Identify the serial interface on your target device.

Check the device manual. Confirm the standard (RS232/RS485/RS422/TTL/console), connector type (DB9, DB25, RJ45, terminal block, pin header), and — for TTL — the logic voltage level. This one step eliminates the majority of selection errors.

2. Match the USB connector to your computer.

USB-A remains common on desktops and older laptops. If your machine has only USB-C, buy the USB-C version directly.

3. Check OS and driver compatibility.

If you're using a recent macOS version or Windows 11 ARM, verify the chipset has stable driver support for your environment.

4. Consider the working environment.

For office and lab use, a standard cable works well. For industrial field use, consider:

• Shielded cable for EMI-heavy environments
• Locking DB9 connectors to prevent accidental disconnection

• Electrical isolation where ground potential differences exist between equipment

Frequently Asked Questions

What is a USB to serial cable used for?

It connects a modern computer — which lacks a built-in serial port — to equipment using RS232, RS485, RS422, TTL UART or console interfaces. Common uses include industrial equipment configuration, network device management and embedded development.

What's the difference between USB to RS232 and USB to RS485?

RS232 is single-ended and point-to-point with a ~15 m range. RS485 is differential, supports multiple devices on one bus and works up to ~1200 m. They are not interchangeable.

Is a USB console cable the same as an Ethernet cable?

No. Both use an RJ45 plug, but a console cable carries serial signals to a device's management port. An Ethernet cable carries network data. They cannot substitute for each other.

Can I use a USB to TTL cable instead of USB to RS232?

No. They use different voltage levels and signal polarity. Using the wrong type risks failed communication and potential hardware damage.

Why does my USB to serial cable not work on macOS?

This is most commonly a driver issue. Check which chipset your cable uses and download the current driver from the chipset manufacturer's website. Prolific PL2303 cables have had known compatibility issues with specific macOS versions.

Summary: Which Cable Do You Need?

Author

Franck Yan
Founder | Farsince Connectivity Solutions

Franck Yan is the founder of Farsince and has more than 13 years of experience in the cable and connectivity industry, working closely with global customers on data center, industrial, and network connectivity solutions.