[Answer] How can a virtual machine access the host's serial port device?

[Answer] How can a virtual machine access the host's serial port device?

There are many differences in the specific steps for this, depending on which virtualization software you use, such as VirtualBox, Hyper-V, or VMware. The detailed procedures vary from one platform to another, but the overall idea is similar. However, in actual implementation, some virtual machines may not be able to achieve the desired result because they lack certain features. Therefore, my personal recommendation is to use VMware whenever possible, since VirtualBox is somewhat less stable by comparison, while Hyper-V, in my view, lacks some functionality.

Generally speaking, after installing a virtual machine, if you want it to communicate directly with external hardware, you need to install the enhancement tools or integration packages provided by the platform (such as those for VMware and VirtualBox). If you are using a dedicated communication card, then both the virtual machine and the physical host may need the corresponding drivers installed. I have not personally tried making a virtual machine work together with a specialized communication card, so I will not go into detail on that.

If you are using a serial port or a USB-to-serial device, the virtual machine software is usually designed with options to assign hardware resources to the VM. Select the resource you want to allocate to the virtual machine, such as a specific serial port or USB port, and then that resource will become available inside the VM. After that, the remaining operations are essentially the same as on a physical machine.

If network communication is used instead, the approach is quite different from the above. When using a virtual machine's network adapter, you need to pay attention to how the host machine's network connection is configured: NAT forwarding, bridged mode, or virtual routing. Under different modes, the virtual machine will have different IP addresses. In some connection modes, the virtual machine may not be able to access the external network at all, while in others it may fail to meet the common requirement of devices such as PLCs that communication must occur within the same subnet as the host computer. There are many online resources explaining the various network connection modes for virtual machines, so I will not elaborate further here.