With the expansion of network technologies we have somehow got used to the fact that even process stations (PLC) communicate with development tools, visualization and other clients via network interface, ie Ethernet with TCP/IP protocol, over which the application protocol is standard (eg BACnet) or manufacturer specific. In addition to high transfer rates, this technology offers low cost, standard interfaces and high technology know-how. A huge advantage is the possibility of remote access and use of the Internet at no extra cost, which saves time during commissioning and service.
But sometimes we get into a situation where the only way to connect two or more controllers to each other or to the headquarters is a serial line – a two-wire line.
What are the most common cases? FULL ARTICLE HERE.