I have just finished a blog post in which we have installed a USB-485M adapter. Here is some of the post...

The USB-485M is a 2-wire USB to RS-485 serial communication adapter for RS485 use. It does not require an external power supply or complicated configuration.

It has a Type A (plug) USB connector for the computer side and a universal female RJ45/RJ12 modular connector. This will accept RJ12 and RJ45 plugs. The USB-485M supports multiple baud rates and is USB V2.0 Compliant.

Installing the Driver
Do NOT connect the USB-485M to your PC before installing the driver file.

Go to the Automation Direct website and download the latest drivers for this device. I would not use the mini CD that came with the converter because it may be out of date.
USB-485M Serial Converter Support Resources

Read the rest of the blog post...

Let me know what you think.
Thank you,