What is the function of RS 485 connection?

Answer 1

The symmetrical pin layout of the RJ11 sockets on the Unitronics PLCs allows an easy way of interconnecting the PLCs with both RS232 and RS485 communications. For RS232a crossover cable is used where pin 1 is connected with pin 6 at the other connector, pin 2 with pin 5, etc. This interconnects the transmit and receive signals of both PLCs, and also the handshaking signals DTR and DSR. If handshaking is not necessary, an ordinary 4 wire telephone cable could be used, provided that the pins are cross-connected as shown in the picture below. Otherwise a full 6 wire cable must be used. Two wire telephone cables will not function because in that case the ground signal levels on both sides will be floating. Unitronics RJ11 RS232 crossover cableRJ11 plug 1RJ11 plug 2Function16DTRDSR25Signal ground34TxDRxD43RxDTxD52Signal ground61DSRDTR

RS485 is in its design a different interface from RS232. The RS485 interface allows the creation of multipoint networks. The normal way to implement this is with a two wire system with differential signal levels. These signals are commonly called A and B in RS485 systems. The A signals of all devices should be connected with each other and the same goes for the B signals. Therefore for RS485 communications no crossover cable is used. To prevent noise to interfere with the communications, often twisted pair cable is used. The diagram below shows a basic RS485 cable for use with the RJ11 socket on Unitronics PLCs. You can easily connect more devices by splitting the cable at one connector and adding another cable to it.Unitronics RJ11 RS485 cableRJ11 plug 1RJ11 plug 2Function11A (+)A (+)

Answer 2

RS-485 is a two wire serial protocol.