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Converters between RS-485 and RS-232 are available to allow a personal computer to communicate with remote devices. RS-485 is also used in building automation as the simple bus wiring and long cable length is ideal for joining remote devices. In theatre and performance venues, RS-485 networks are used to control lighting and other systems using the DMX512 protocol. Although many applications use RS-485 signal levels, the speed, format, and protocol of the data transmission are not specified by RS-485. DH 485 is a proprietary communications protocol used by Allen-Bradley in their line of industrial control units. RS-485 is used for low-speed data communications in commercial aircraft cabins' vehicle bus. In contrast to RS-422, which has a driver circuit which cannot be switched off, RS-485 drivers use three-state logic allowing individual transmitters to be deactivated. For an off, mark or logic 1 state, the driver's A terminal is negative relative to the B terminal. For an on, space or logic 0 state, the driver's A terminal is positive relative to the B terminal. If A is negative with respect to B, the state is binary 1. The reversed polarity (A positive with respect to B) is binary 0. The standard does not assign any logic function to the two states.

Polarity of the wires must be observed. This section also defines the logic states 1 (off) and 0 (on), by the polarity between A and B terminals. Because a mark (logic 1) condition is traditionally represented (e.g. in RS-232) with a negative voltage and space (logic 0) represented with a positive one, A may be considered the non-inverting signal and B as inverting. Line A voltage, implying A, the green wire, is indeed connected to the driver inverting signal, as seen in a whitepaper. End of line termination resistor (120 ohm 1/4 watt) to be installed at both ends of network. The value of each termination resistor should be equal to the cable characteristic impedance (typically, 120 ohms for twisted pairs). The capacitance is close to 12.5 pF/foot but there is a small impedance mismatch (100 ohms for Cat 5, 120 ohms for RS-485). 24 AWG solid wires, which are typically used in Cat 5 cables, can break easily when connected to a screw terminal block, which does not provide any strain relief.

RS-485, like RS-422, can be made full-duplex by using four wires. RS-485, also known as TIA-485(-A) or EIA-485, is a standard, originally introduced in 1983, defining the electrical characteristics of drivers and receivers for use in serial communications systems. Splicing of communications cable is not permitted. The most common cable type is Cat 5e-UTP (unshielded twisted pair) which may work over shorter distances in less demanding applications with low EMI noise levels. 60%, rs485 cable UL Type CMP/CL3P 24 AWG. Termination resistors also reduce electrical noise sensitivity due to the lower impedance. This way, the lines will be biased to known voltages and nodes will not interpret the noise from undriven lines as actual data; without biasing resistors, the data lines float in such a way that electrical noise sensitivity is greatest when all device stations are silent or unpowered. Failure to stay within this range will result in, at best, signal corruption, and, at worst, damage to connected devices. Ideally, the two ends of the cable will have a termination resistor connected across the two wires.

In practice, Cat 5 cables have been used successfully in many installations, but there are some concerns. Category 5 (Cat 5, Cat 5e, and Cat 6) cables are the most common Ethernet cables in use today. The EIA has officially disbanded and the standard is now maintained by the TIA as TIA-485, but engineers and applications guides continue to use the RS-485 designation. RS-485 standard conformant drivers provide a differential output of a minimum 1.5 V across a 54-Ω load, whereas standard conformant receivers detect a differential input down to 200 mV. The WattNode® BACnet and Modbus® meters communicate using RS-485 (TIA/EIA-485-A) half-duplex, differential signaling at 9600, 19200, 38400, and 76,800 baud. RS-485 supports inexpensive local networks and multidrop communications links, using the same differential signaling over twisted pair as RS-422. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. By using repeaters very large RS-485 networks can be formed.