![]() Unitronics PLC pin assignment for the RJ11 socket When the DSR and DTR signals are not used, the two pins can be used for simultaneous RS485 communication. ![]() On some PLC models it is possible to mix RS232 and RS485 communications. These pins are normally used for the DTR, data terminal ready and DSR, data set ready signals. Pin 1 and 6 however are reassigned to the A and B lines when the port is used in RS485 mode. When in full RS232 mode, the six available pins are assigned to the most used RS232 signals. The existence of an RS485 port on the socket makes it even a little bit more difficult. It shouldn’t however be a surprise that the pin assignment on the RJ11 socket on Unitronics PLCs is different from the two systems mentioned above. A symmetrical pin-layout allows two DTEs, data terminal equipment, to be connected directly without use of a modem or other DCE, data communication equipment. The RJ11 socket is interesting, because the manufacturer choose to have a symmetrical pin-layout, just as with the MMJ connector on DECconnect systems and the RJ45 jack in the Yost standard. The actual functionality is determined by DIP-switches on the mainboard of the PLC. The RJ11 connector can be used for both RS232 and RS485. These ports use an RJ11 socket as physical connector. For communications, many of their products are equipped with an RS232 or RS485 serial port. Unitronics is a PLC-manufacturer based in Israel.
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