Connect correctly the communication ports of rs 485 between both plcs.
Arduino rs485 beispiel. Check out the detailed tutorial on rs 485 modbus serial communication with arduino as master. This library supports the maxim integrated max3157 and equivalent chipsets. In half duplex mode it has a data transfer rate of 2.
Next we will proceed to explain how this example works. Our rs422 rs485 serial shield is a fully galvanic isolated serial communication hat designed for use with the arduino uno and other compatible boards like arduino 101 stm nucleo. Rs485 library for arduino enables sending and receiving data using the rs485 standard with rs485 shields like the mkr 485 shield.
More details about rs 485 modules here. Simplecomm libraries installed on your arduino ide. Its possible to use an arduino as slave and with some restrictions also as master in modbus applications but a rs485 interface is needed.
See on rs 485 communication. Rs 485 example communication and how to use our libraries. There is also a usb to rs485 module top right for use on pc s.
See the example rs485 network diagram scroll down. How to install simplecomm libraries. See rs485 example of two arduinos communicating over re 485 here.
For using rs 485 in arduino a module called 5v max485 ttl to rs485 which is based on maxim max485 ic is needed as it allows serial communication over long distance of 1200 meters and it is bidirectional. The network has 120 ohm termination resistors at each end. The example here shows two arduinos connected with low cost rs485 electronic bricks or breakout boards that use a max485 chip.
It can be used between 2 or more arduinos and to various i o devices that support it.