The question on the origin of RS485 may sound odd ! Let me explain - if you take the RS232 its a complete thing, in the sense it defines both the physical layer as well as the handshake protocols etc. So to connect two devices you just needed that .
Cut to RS485 .. immediately MODBUS raises its head !! Almost to an extent that people ( or atleast me ) believe that Modbus is always over RS485 . Some rare cases we have RS232 endpoints linked via RS 485 to take advantage of the relatively better noise immunity.
Where else is RS485 used ? Like can I realize one master and many slaves linked with RS485 ... all with proprietary coding NOT using Modbus. ( I have nothing against Modbus anyway - just a hypothetical query !!)
I used RS485 when I worked in the access control industry, to communicate with several door access control modules and gather the access log and download new access tokens to the door controllers that needed them. All this over a range of half a mile or so.
RS-485, also known as EIA-485, is a standard for serial communication in electrical engineering. It was developed by the Electronic Industries Association (EIA) in the 1980s and is widely used in industrial automation and control systems, as well as other applications requiring reliable long-distance data transmission.
The origin of RS-485 can be traced back to its predecessor, RS-232, which was developed in the 1960s by the EIA. RS-232 was primarily designed for short-range serial communication between devices, typically within a few meters. However, as the need for longer distance communication in industrial environments arose, RS-232 became less suitable due to its limitations in noise immunity, data rate, and cable length.
To address these limitations, the EIA developed the RS-485 standard. RS-485 is a differential bus standard, meaning that it uses two wires for data transmission, one for the positive signal (A) and the other for the negative signal (B). This differential signaling method provides improved noise immunity and enables communication over longer distances, reaching up to 1.2 kilometers or more.
RS-485 supports multi-drop communication, allowing multiple devices to be connected on the same bus using a master-slave configuration. It can operate at data rates ranging from a few hundred bits per second up to 10 Mbps, depending on the cable length and the quality of the transmission media.
The RS-485 standard has gained widespread adoption due to its robustness, simplicity, and versatility. It is commonly used in applications such as industrial automation, building automation, process control, and instrumentation. It provides reliable and cost-effective communication over long distances, making it suitable for various industrial and commercial environments.
For direct communication between peers the specs are so weak that it can take days to establish a reliable connection using device specific hardware and software.
Easy connection has to be restricted to RX and TX lines only, with XON/XOFF handshake if required. That's what RS-485 or any other line drivers offer as well.
Ah. Nope. The most obvious example is that you can run synchronous protocols like HDLC over RS232. The "handshake protocols" that you think are standard are probably hacks that were never in the original standard, and you probably aren't aware of the uses of all those other pins on the DB25 connector...
Thanks to all those who posted responses and also shared some use cases with no Modbus being invited !!
Sure Google or Wiki are there but its like a AK47 firing as compared to the forum posts which is like a hand gun at point blank range - save so much time
I thought i should add that one of the most common applications is DMX lighting control which is the industry standard for clubs and theatres. Also to find out how long the twisted pair wires have been around as solution, googl/wiki that.
