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2025-03-06 17:47:59 R. Bishop: Initial Commit| /dev/null .. communications/serial/rs485.md | |
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| + | # RS-485 (Recommended Standard 485) |
| + | |
| + | ## What is RS-485 and why should we care about it? |
| + | RS-485 is a standard which defines the electrical characteristics of drivers and receivers for serial communications systems. RS-485 is commonly found in industrial & security systems as it allows multiple devices to be connected together over long distances with very simple wiring. Unfortunately, even though RS-485 is wide spread throughout the industry, there's often an observable lack of understanding as to how it works and how it should be connected which we will try to address below. |
| + | |
| + | --- |
| + | |
| + | ## History of RS-485 |
| + | The standard as we know it was initially introduced back in 1983 by the Electronic Industries Alliance (EIA) back when the standard was first introduced the EIA labelled all of its standards with RS (Recommended Standard). As of today, the EIA has disbanded and the standard is now maintained by the Telecommunications Industry Association (TIA) as TIA-485, however it's original designation of RS-485 is still widely preferred by manufacturers and engineers alike. |
| + | |
| + | --- |
| + | |
| + | ## What is serial communication? |
| + | Put simply, serial communication is a method of sending data between multiple devices by transmitting bits one at a time utilisting a single wire or channel. |
| + | |
| + | **How it works** |
| + | - Data is sent in a packet or "frame" of bits. |
| + | - The receiver interprets the voltage on its wire as a bit of data. |
| + | - A high voltage is interpreted as 1 and a low voltage is interpreted as 0. |
| + | - The reciver interprets the bits of data over time to get a message from the sender. |
| + | |
| + | For more information on Serial Communication please see our explanation page [HERE](https://) |
| + | |
| + | --- |
| + | |
| + | ## Full or Half duplex? |
| + | |
| + | **Well firstly, what do we mean by duplex?** |
| + | |
| + | A duplex communication system refers to any point-to-point (PTP) system composed of two or more connected devices which can communicate with each other in both directions. There are two common duplex communication systems: Full-Duplex (FDX) and Half-Duplex (HDX). |
| + | |
| + | In a **Full-Duplex** system, communication can occur in both directions simultaneously. Old-style telephone service lines are a prime example of an FDX communication system; both parties are able to speak and be heard by the other party simultaneously, there is a constant channel each way between them. |
| + | |
| + | In a **Half-Duplex** (also known as a **semiduplex**) communication can only occur one way at a time. If device A would like to send data to device B, but device B is already sending data to device A, then device A will have to wait until device B has stopped transmitting to send data. |