While with RS232 many devices simply use text (ASCII) protocols, with RS485 most devices use the MODBUS protocol. The main particularity when using RS485 is in the format of the exchanged data. It's cheaper and it's one less component in the system. There are indeed RS232 to RS485 gateways, but they are not interesting nowadays: it's as easy to use an RS485 to USB, to Ethernet, or to GSM directly. RS485 and RS232 are not directly compatible: you must use the correct type of interface, or the signals won't go through. Sometimes this means that you must screw a small resistance on a terminal, or simply move a switch in the adequate position.Īn RS485 bus is often made of just two wires and a resistor at the extremities. However, there is a small trick to do so: at each end of the bus, you must put a bus terminator. Therefore, you don't have to multiply RS485 interfaces on the host to question several devices. An important advantage of RS485 is that you can put several RS485 devices on the same bus. RS485 is a serial transmission standard, a little bit like RS232, but using other electric signals. While exchanging with our customers on the best ways to interface industrial controllers, we noticed that nowadays the small secrets enabling you to use an RS485 interface were sometimes unknown from engineers implementing computer or internet based automation. Here is an excerpt from Wikipedia: RS-485, also known as TIA-485 (-A) or EIA-485, is a standard defining the electrical characteristics of drivers and receivers for use in serial communications systems. The RS485 standard is widely accepted in industrial automation along with the Modbus RTU protocol.

The document was generated in response to repeated questions from the field. of 35 RS485 Guide 07/02 Rev 6 Introducing the MODBUS Protocol This document is intended to provide an introduction to the MODBUS implementation of Integra and SPR products. When the COMMAND CENTER communicates with the Analyzer, go to the VARIABLES. Open the COMMAND CENTER and initiate communication with the Analyzer.

Modbus RTU Protocol over RS485 Communications The Modbus address is entered in variable N1 for the Analyzer.

The protocol interconnects field equipment such as sensors, actuators, and controllers and is widely used in both process and manufacturing automation.

Modbus RTU is an open, serial (RS-232 or RS-485) protocol based on master/slave or client/server architecture.

Cable Termination (RS485/Modbus RTU Line Line Bias) When the RS485 network is not being actively driven by a device the differential pair is more susceptible to interference and noise.

Networks in a high RF environment may require the use of Line Bias (see next section: CABLE TERMINATION, RS485 / MODBUS RTU LINE BIAS) to stabilize communications.

Modbus rtu protocol example