COM port in Virtual Machine - An Extended Guide

Updated: Nov 27, 2024

To establish a connection between a physical COM port device and a VM, a serial port in virtual machine is necessary. Think of it as a virtualized interface that imitates a physical port on a physical computer. Successful setup of this “virtual” serial port will provide remote access to COM port devices via your VM.

However, serial port passthrough in VM is often far from easy. Several problems can arise due to the complexities of virtualization technology or hardware incompatibility.

Contents

How to Enable COM ports in a Virtual Machine
Issues that Arise While Connecting Serial Port to VM’s

How to Enable COM ports in a Virtual Machine

Here are easy-to-follow steps to share a local serial port on a virtual machine using Serial to Ethernet Connector software:

1

On the computer that will share the COM port (host) download, install and launch Serial to Ethernet Connector.

Select your OS on the website, download the installer and run it

2

Open the "Server connection" tab. Define the COM port on the host and the TCP port that will be used to monitor the communication. Click the "Create server connection" button.

Select “Server connection” and choose Telnet in “Network settings”

3

On the guest operating system configure the host’s IP address and the TCP port that you defined when you created the server connection.

Choose “Client connection” on the remote machine

4

Select the name to be used by the virtual machine’s serial interface before enabling the "Create as virtual serial port" option. Click the "Create client connection" button.

Your new connection can be seen in the list on the left

Issues that Arise While Connecting Serial Port to VM’s

Whether you’re a Hyper-V, VirtualBox, or VMware user, you’re still bound to experience issues due to improper setup processes or inherent limitations of the virtualization technology.

To effectively perform serial port troubleshooting for VM, you must be familiar with these issues.

VMware COM Port Passthrough Issues

1. Device Conflicts (Multiple Devices on Same Port)

Multiple virtual machines might not function properly if they access the same physical COM port simultaneously.

Cause: Only one device can access a port at a time. Therefore, multiple VMs or applications on a single COM port may lead to device conflicts or incompatibilities.

How to Resolve: Each virtual machine or application should have a unique COM port. Assign VMs or applications to different ports and configure your system so that no two devices have the same COM port.

Note: This applies to all virtual environments.

2. VMware Configuration Challenges (Incorrect Settings)

The virtual machine cannot recognize or use the physical COM port due to incorrect configuration of the COM port passthrough settings.

Cause: Errors in VM setting configuration, such as wrong COM port mappings or improper physical port assignments, can cause failure in COM port passthrough.

How to Resolve: Check your VM settings and ensure the port numbers match the host and guest OS.

3. Performance Issues (Latency and Throughput)

Latent or degraded performance of the COM port passthrough may result in a slow and unreliable connection between the VM and hardware.

Cause: Heavy workloads in the VM or resource contention on the host system may adversely affect the rate of serial communication.

How to Resolve: Ensure that your host and VM have sufficient CPU and memory allocation. You can also optimize the VM configuration for enhanced allocation of hardware resources.

4. Limited COM Port Support in Some VMware Products

Some VMware products, such as VMware Workstation or VMware ESXi, have a limited number of COM ports that can pass through a VM.

Cause: The VMware version or edition has built-in limitations or restrictions on the number of serial ports available for passthrough.

How to Resolve: Upon confirmation that your VMware has COM port support limitations, upgrade it to a version or edition that supports additional serial ports, or consider using alternate tools to address your needs.

VirtualBox COM Port Passthrough Issues

1. Incorrect COM Port Configuration or Mapping

If the physical port is incorrectly mapped to the VM, the system may fail to detect or use the serial device.

Cause: Misconfiguration in VirtualBox’s settings or mappings can result in the VM's failure to recognize the assigned COM port from the host system.

How to Resolve: Check the VirtualBox settings under the "Serial Ports" tab and ensure that the host COM port is correctly mapped to the VM. Verify the configuration and ensure that the correct post is used in both VirtualBox and the guest OS.

2. USB-to-Serial Adapter Compatibility Issues

VirtualBox often fails to recognize or properly use USB-to-serial adapters, resulting in communication failures.

Cause: If the USB-to-serial adapter is incompatible with VirtualBox, or if the necessary drivers are not installed in the guest OS, the system may not be able to detect the devices.

How to Resolve: Use compatible USB-to-serial adapters and ensure they are properly configured in VirtualBox. Also, make sure to install the appropriate drivers in the guest OS to allow the USB device to be recognized.

3. COM Port Performance Issues

Poor throughput or latency in COM port passthrough can result in delays or instability in serial communication.

Cause: If the VM does not have sufficient resources to handle serial communication, it may cause instability in the VirtualBox system.

How to Resolve: Make sure that the VM has adequate CPU and memory allocation. Optimize its settings to improve performance and reduce latency for high-level applications.

Hyper-V COM Port Passthrough Issues

1. Limited Native Support for COM Port Passthrough

Hyper-V’s interface is not straightforward or user-friendly, which makes the configuration of COM port passthrough more challenging compared to other hypervisors.

Cause: Hyper-V’s lack of native and easy-to-use tools for COM port passthrough management forces users to rely on inefficient methods such as PowerShell commands or manual file configurations.

How to Resolve: Use third-party software (like Serial to Ethernet Connector) to simplify the passthrough configuration process, or follow detailed guides carefully to set up the VMware COM port passthrough using PowerShell commands.

2. Complex COM Port Passthrough Configuration and Setup

COM port passthrough configuration in Hyper-V entails advanced configuration methods such as PowerShell commands or manual editing of VM configuration files, which can be too complex for inexperienced users.

Cause: Hyper-V has no graphical interface for COM port configuration, so users need to manually enter commands or edit configuration files.

How to Resolve: Use pre-configured scripts or enlist help from virtual COM port software tools to simplify the configuration process.

3. Compatibility Issues with COM Port Support Limitations in Some

USB-to-serial adapters do not always work properly with Hyper-V. Additional configuration steps may also be required to avoid communication instability.

Cause: Not all USB-to-serial adapters are compatible with the system, and Hyper-V’s USB passthrough functionalities are limited.

How to Resolve: Use known compatible USB-to-serial adapters and ensure that the USB passthrough is properly configured. You might also need to install some necessary drivers on both the host and the guest OS for stable communication.

So, is it possible to solve these VM problems? With a well-designed and robust virtualization software, the answer is a resounding yes!

High-quality software solutions, such as Serial over Ethernet, provide better compatibility, an intuitive UI, comprehensive documentation, and dedicated support, which leads to a smoother and more reliable VM experience.

Try Serial over Ethernet now

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How to series:

How to access COM port on the Amazon Web Services VM

Learn how to access a serial port in a virtual machine: using Serial to Ethernet Connector by Electronic Team, Inc. to access a GPS sensor plugged into a physical COM port from a VM powered by Amazon Web Services via an RDP connection.

How to use COM port in Hyper-V to access a GPS sensor

Find out how to set up Hyper-V serial port passthrough. Serial to Ethernet Connector by Electronic Team, Inc. can forward a real COM to a virtual machine via the RDP connection so you can use a device connected to it, e.g., a GPS sensor.

Connect GPS sensor - VirtualBox COM port passthrough

Using a COM-based device in VirtualBox: With Serial to Ethernet Connector by Electronic Team, Inc., you can set up VirtualBox serial port passthrough via the RDP connection and read data from a GPS sensor on your virtual machines.

VMware serial port passthrough

Accessing a COM port in VMware: setting up serial port passthrough to multiple VMs. Using Serial to Ethernet Connector by Electronic Team, Inc. to connect a real COM port in VMware and read data from a GPS sensor connected to that port on two virtual machines.

Wrap Up

To sum up, VMs are an innovative and efficient solution to run multiple operating systems and programs on a single host. They can also access devices connected to COM ports via virtual serial ports.

However, users often experience COM port passthrough issues due to device incompatibility or poor configuration. By choosing high-quality virtualization software, these problems can be mitigated, ensuring seamless remote access and management.

Try Serial over Ethernet today to easily access a serial port virtual machine, share COM ports over the network, and connect to remote serial devices like they were physically attached to your local PC.

Serial to Ethernet Connector

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