RS-485 signals are used in a wide range of computer and automation systems. In a computer system, SCSI-2 and SCSI-3 may use this specification to implement the physical layer for data transmission between a controller and a disk drive. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. It requires minimal wiring and can share the wiring among several seats, reducing weight.
RS-485 is used as the physical layer underlying many standard and proprietary automation protocols used to implement Industrial Control Systems, including the most common versions of Modbus and Profibus. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. Utilizing a series of dedicated interface devices, it allows PCs and industrial controllers to communicate in a local area network utilizing a token passing medium access control. These are used in programmable logic controllers and on factory floors. Since it is differential, it resists electromagnetic interference from motors and welding equipment.
In theater and performance venues RS-485 networks are used to control lighting and other systems using the DMX512 protocol.
RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. It may be used to control video surveillance systems or to interconnect security control panels and devices such as access control card readers.
It is also used in model railway: the layout is controlled by a command station using Digital Command Control (DCC). The external interface to the DCC command station is often RS-485 used by hand-held controllers or for controlling the layout in a network/PC environment. Connectors, in this case, are 8P8C / RJ45.
Although many applications use RS-485 signal levels; the speed, format, and protocol of the data transmission are not specified by RS-485. Interoperability of even similar devices from different manufacturers is not assured by compliance with the signal levels alone.