Both the generator (driver) and the receiver of all devices on the network are connected to the two wires. Two circuits are for transmitting and receiving the serial data, circuit "BA" (TX data on pin 2) and "BB" (RX data on pin 3). A number of circuits are for handshaking and other functions. 0.2V the receivers output switches to a 1 and when the voltage goes below -0.2V the receivers output switches to a 0. (or vice versa if there is inversion on the receiver) Since the last bit from a UART will be the stop bit (1), then the transmitter is turned off (the differential voltage goes to 0V, but not having gone less than -0.2V), this should leave the receiver with a 1 being output to the receiving UART. Yet the signaling waveforms in Figure 1 of the RS-485 standard clearly show that when a binary 0 (ON) is on the wires, the voltage on wire "A" is positive with respect to "B" and conversely, when a binary 1 (OFF) is on the wires, the voltage on wire "A" is negative with respect to "B". The "idle" state (MARK) has the signal level negative with respect to common, and the "active" state (SPACE) has the signal level positive with respect to common.

Implementing this requires a higher level addressing scheme so the data being transmitted goes to the correct device. Digital communications networks implementing the standard can be used effectively over long distances and in electrically noisy environments. Another implementation of two RS-485 networks is BitBus, which uses one of the RS-485 networks for bidirectional SDLC data communications (very different from asynchronous start-stop communications with a UART), and a second, optional, RS-485 network for RTS (direction control if a repeater is used). When two pair of wires are used for full-duplex communications, one pair is used for the interface generator (driver) to talk to the other device(s) on the RS-422 network, and the second pair is the interface receiver used to listen to an other device (not devices, since only one driver can be on this pair of wires) on the network. In its simplest form, a pair of converters from RS232 to RS422 (and back again) can be used to form an "RS232 extension cord." Data rates of up to 100K bits / second and distances up to 4000 Ft. The annex discusses the fact that many applications can handle greater amplitude and timing distortion, and that practical experience has shown that the cable length can be extended to several kilometers at lower data rates.

A byproduct of the differential voltage system is the extended data transfer distance, increased transmission speed, and lower voltage use seen with RS485. 5V is shown in the figure since many drivers are powered by 5Vdc. Other pull-up voltages can be used and it is not an absolute requirement that the pull-up voltage match the driver's supply voltage. RS-485 voltages are referenced differentially from one wire to the other, but are also referenced to circuit common. If this is required, it can be accomplished by any means desired including RS-485 drivers on an additional network, RS-232 drivers on extra wires, TTL levels, or really anything you can dream up since it won't work with any other RS-485 network except the one you are designing. It is NOT necessary to introduce long delays in a network to avoid "data collisions." Because delays are NOT required, networks can be constructed, that will utilize the data communications bandwidth with up to 100% through put. RS422 devices. These networks are often used in a half-duplex mode, where a single master in a system sends a command to one of several "slave" devices on a network. Systems of this type (4-wire, half-duplex) are often constructed to avoid "data collision" (bus contention) problems on a multi-drop network (more about solving this problem on a two-wire network in a moment).

Single master systems (many other communications schemes are available) offer a straight forward and simple means of avoiding "data collisions" in a typical 2-wire, half-duplex, multi-drop system. These characteristics make RS-485 useful in industrial control systems and similar applications. The RS-485 standard has very little to say about grounding. The RS-485 standard is obsolete and has been superseded by TIA-485, but many if not most engineers and applications guides continue to use the RS designation even though it has officially changed. RJ45 connections are used for RS-485 frequently, due to the ease of using the modular connectors and availability of cables and connectors. Also, RS485 drivers are able to withstand "data collisions" (bus contention) problems and bus fault conditions. The difference between an adapter and a converter generally is that an adapter usually only adapts the physical interface of a device to match a different type of physical interface of a different device whereas a converter converts the actual data stream between two devices. Now, let’s take a look at the main differences between the two protocols.

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