• Home
  • Blog
  • Which Type of Modbus Splitter Do You Need?

Which Type of Modbus Splitter Do You Need?

avatar
Written by
Updated on: September 1, 2026
Time to read: 8 minutes

Modbus splitters are available in three forms, each designed to address different use cases. We will examine all three options to help you choose the right one. In some cases, a physical Modbus RS485 splitter is all you need, while in other scenarios, a software solution makes more sense.

The following three types of Modbus data splitters are commonly available.

• A passive splitter is a physical device that branches an RS485 cable so multiple devices can use the signal in proximity.
• An active splitter is a powered device that isolates and regenerates the Modbus signal for use to minimize electrical noise in larger networks.
• A software splitter allows multiple applications to share a Modbus port simultaneously. It does not support two physical Modbus masters sharing the same RS485 bus.

Physical Modbus Splitters

Physical Modbus splitters can be either passive or active. Each type serves a different purpose.

Passive Splitters such as Hubs or Y-Adapters

A passive splitter is an unpowered device that splits a single RS485 feed into several lines and is typically used in small implementations where the target devices are close together. It adds no active components and does not extend the effective cable budget. The combined network is still subject to the RS485 standard limits of ~1200 m and 32 devices. These features make a passive splitter a good choice for compact installations such as hard drive cabinets. It is not appropriate for long branch stubs or when mixing devices from multiple manufacturers with different termination factors.

A passive splitter will not work if you require power injection. They only distribute the signal, not boost it. Simple RJ45-based passive hubs can be obtained for around $50. A more elaborate passive Modbus splitter, such as the Schneider Electric LU9GC3 splitter block, costs around $400 and can connect up to 8 devices to a single PLC.

When purchasing a passive splitter, you should verify several factors.

• The number of port/branches you need, as they typically support from 3 to 10.
• The connector type used, which can be a screw terminal, RJ45, or a DIN-rail terminal block to integrate with your existing wiring.
• Whether you need to add termination resistors at the end of each branch or if they are built into the device.

Active Splitters such as RS485 Repeaters or Isolators

An active splitter is a powered device that regenerates the signal and adds isolation. They are typically used for long cable runs and in large, noisy networks. Active splitters do not just distribute the Modbus signal. They regenerate the signal so that each branch becomes a separate RD485 segment with termination and device-count limits. These features support running longer cables to more devices than a passive splitter. 

The signal isolation available in active Modbus splitters helps protect a master device from ground-loop damage due to an electrical ground fault on a slave device. An active splitter uses its own power supply and is usually deployed when a passive splitter cannot handle the number of devices or the required distance. A typical repeater/converter capable of isolation, such as the RPT-485_422-4, extends the bus by up to 1.2 km with 2.5kV isolation and runs around $120. The cost increases if you need additional protocol conversion or greater isolation voltage. 

Check the following factors when buying an active Modbus RS485 splitter.

• Most active splitters require an external  9–30VDC power supply.
• Common isolation voltage is 2.5kV, but you may opt for 3–4.5kV for harsher electrical environments.
• Whether the device automatically senses the data format and baud rate or needs to be configured to integrate with your other devices.

Software Modbus Splitter

Windows restricts access to serial ports to one application at a time. A software splitter overcomes this limitation, allowing multiple programs to read Modbus data from the same port simultaneously. Next, we take a closer look at Virtual Serial Port Driver PRO, a feature-rich software Modbus splitter.

Virtual COM Port Splitting

The dedicated solution – RS485 Splitter – will let you create virtual RS485 ports and split Modbus data in such a way that all ports will receive the same data simultaneously. This means you’ll be able to duplicate data coming in on COM1 to say virtual COM2, COM3, COM4, and so on. Connected to virtual copies of COM1, several apps will, in fact, get shared access to the real serial port.

Virtual Serial Port Driver PRO lets you split and join serial ports used by RS485, RS232, and RS422 devices, redirect the data from one port to another, and create complex port bundles.

With this Modbus data splitter software, you can have as many virtual COM interfaces as you need. What is especially important is that all of them will completely emulate the parameters and configuration of the original hardware ports.

Note:  VSPD PRO can also join multiple ports into one, build many-to-many port bundles, or auto-switch between real ports — see our Modbus Software guide for more.

Step-by-Step Guide

To split one physical RS485 port into several virtual ones, follow these simple steps:

1. Download Virtual Serial Port Driver PRO and install it on your machine.

2. Start the app. Open the “Split” tab and select “Split real port”.

Bundle tree

3. Select the real port that needs to be duplicated, add virtual ports (that will communicate with the split real port) by clicking the “Plus” button. You can create and add as many virtual ports as you need.

4. Choose a virtual port to set as main in the bundle and click “Set main”.

5. Finally, click the “Create” button and your COM port bundle will automatically appear in the Bundle tree.

That’s it! Now, Modbus data coming into the real serial port will be sent to all virtual ports and applications connected to them.

Also, as an alternative to splitting serial data, the solution can help you share one real port among multiple applications and set the access rights (“Read”, “Write”, and “Control”) for each of them.

How to Select the Right Modbus Splitter for Your Use Case

Use this simple guide to determine the type of Modbus splitter you need. 

• Choose a software splitter if you have multiple applications on a single PC that require access to the same Modbus port.
• Select a passive splitter when you want the Modbus signal to reach nearby devices over short branches.
• Use an active splitter to support more devices, long cable runs, and to provide electrical isolation for noise reduction. 

Common Modbus Splitter Use Cases

We match the following common use cases with the right type of Modbus splitter.

• Two SCADA systems monitoring a single PLC require a software splitter.
• A PLC, SCADA, and historian that need access to the same port require a software splitter.
• To share the Modbus signal with several devices in the same cabinet, use a passive splitter.
• Supporting extensive production lines with widespread devices requires an active Modbus splitter.

Software vs. Hardware

This table summarizes the differences between the three types of Modbus Splitters.

  Passive splitter  Active (RS485) splitter  Software splitter (VSPD) 
Use case  Branching a single cable to several devices  Extending or isolating a signal across a large bus and multiple devices  Enabling multiple apps running on one PC to read the same COM port 
Powered  No  Yes N/A (software)
Typical cost  ~$20–$100  ~$100–$400+  License-based, from $199.95 
Where the splitter resides  On the RS485 wiring  On the RS485 wiring  On the Windows machine 
Limitations  Does not resolve software port contention  Does not resolve software port contention  Cannot resolve physical bus/master conflicts 

Conclusion

The three types of Modbus splitters are designed to address three use cases. Using the wrong type of splitter will not produce acceptable results. When you need to reach nearby devices over a short branch, a passive splitter is the right choice. If you need isolation or are supporting a long, noisy bus, choose an active physical splitter.

When wiring is not the issue, but you need to have multiple Windows applications open the same COM port at once, you need a software splitter. Virtual Serial Port Driver PRO is a simple solution that resolves the problem with a few clicks. It lets you accurately replicate data from a physical port to as many virtual ports as your applications need.

FAQ

Yes, if you want to split the data to support multiple applications on the same computer that must access the machine’s COM port. A virtual port driver, such as VSPD PRO, does not affect the physical wiring; it simply duplicates the incoming data across multiple virtual ports.

No, they are essentially the same thing since Modbus RTU is the protocol running over an RS485 physical layer. The terms “Modbus RTU splitter” and “Modbus RS485 splitter” are often used interchangeably since both split an RS485 serial line.

They can, but require dedicated hardware designed for multi-master arbitration. You still may experience timeouts with this type of setup. A passive splitter is not sufficient to manage bus contention between two masters.