There are broad range of OEM companies that make these low cost converter devices that function to convert USB to RS485 and RS422 standards. RS485 and RS422 are communication standards that are suitable for harsh environments where there may be a lot of electrical interference from other devices and machines. These standards are half duplex transmission meaning that the only one communication is being done at a time using 2 wires. Using 4 wires full duplex can be achieved.
Many of these OEM device boards also have jumper settings or software that can change the mode between RS-232/RS-422/RS-485.
Some of the most common RS485/RS422 compliant devices may use one of the following chipsets:
- FTDI FT232BL
- FTDI FT232RL
- FTDI FT2232HQ
- Prolific PL2303
- Prolific PL2303EA
- Silicon Labs
- Silicon Labs CP2102
- Silicon Labs CP210x
- Silicon Labs CP2108
Each chipset has its own drivers, and each brand that uses one of these chipsets have their own packaged drivers to create a virtual comms port on the operating system so an application can use the device.
There is generic driver packages on the chipset makers websites that may serve as a solution if the OEM of your device doesn't have a driver or doesn't support the operating system that you intend to use. Below are links to drivers that you can use as a last resort if you can't find what you are looking for.