networks//network protocols//RS-485
An electrical standard for serial communication over a differential pair (A and B lines), allowing many devices on one multidrop bus over long distances with good noise immunity. It defines the physical and electrical link, not the messages.
An electrical standard for serial communication over a differential pair (A and B lines), allowing many devices on one multidrop bus over long distances with good noise immunity. It defines the physical and electrical link, not the messages.
A typical topology is one master and a daisy chain of devices, each with an address, on a single twisted pair. What the bytes mean is decided by the protocol above: Modbus RTU is the usual one in plants, and PROFIBUS also rides on RS-485 signalling (protocol stack).
It is the cheapest digital field link there is and the reason "digital" never implied "Ethernet": a 2003 flow meter on RS-485 is fully digital and has no IP address (fieldbus).