PLC Communication Cables Configuration and Wiring Diagram

Unitronics PLC interfacing

• RJ11 connector pin assignment
• Basic RJ11 connection cables
• Unitronics RS232 programming cables

RJ11 serial RS232 and RS485 connections

Unitronics is a PLC-manufacturer based in Israel. For communications, many of their products are equipped with an RS232 or RS485 serial port. These ports use an RJ11 socket as physical connector. The RJ11 connector can be used for both RS232 and RS485. The actual functionality is determined by DIP-switches on the mainboard of the PLC.

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. 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. It shouldn't however be a surprise that the pin assignment on the RJ11 socket on Unitronics PLCs is different from the two sytems mentioned above. The existense of an RS485 port on the socket makes it even a little bit more difficult. When in full RS232 mode, the six available pins are assigned to the most used RS232 signals. Pin 1 and 6 however are reassigned to the A and B lines when the port is used in RS485 mode. These pins are normally used for the DTR, data terminal ready and DSR, data set ready signals. On some PLC models it is possible to mix RS232 and RS485 communications. When the DSR and DTR signals are not used, the two pins can be used for simulraneuous RS485 communication.

Unitronics PLC pin assignment for the RJ11 socket

The RJ11 socket in the Unitronics PLCs provides six signal pins. In RS232 mode all pins are used for RS232 signals. When in RS485 mode, only pin 1 and 6 are reassigned. The central four pins remain their original RS232 functionality.

Unitronics PLC RJ11 pin assignment

Pin	RS232 function	RS485 function
1	DTR	A (+)
2	Signal ground	RS232 signal
3	TxD	RS232 signal
4	RxD	RS232 signal
5	Signal ground	RS232 signal
6	DSR	B (–)

Basic Unitronics RJ11 connection cables

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 RS232 a 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 cable

RJ11 plug 1	RJ11 plug 2	Function
1	6	DTR		DSR
2	5	Signal ground
3	4	TxD		RxD
4	3	RxD		TxD
5	2	Signal ground
6	1	DSR		DTR

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 cable

RJ11 plug 1	RJ11 plug 2	Function
1	1	A (+)		A (+)
6	6	B (–)		B (–)

RS232 to Unitronics RJ11 PC programming cables

PCs are normally not equipped with an RJ11 socket for serial RS232 communications. If we want to connect a PC with an Unitronics PLC, for example for programming or debugging reasons, we need a connection cable which is on one side fitted with a female DB9 connector, and on the other side with an RJ11 jack. The layout for this cable is shown below.

Unitronics RJ11 RS232 programming cable

DB9	RJ11	Function
2	3	RxD		TxD
3	4	TxD		RxD
4	6	DTR		DSR
5	2 + 5	Signal ground
6	1	DSR		DTR

The Jazz PLC series from Unitronics are not standard equipped with a RJ11 connector for serial communications. The only way to add RS232 capabilities to the Jazz PLCs is by using the MJ20-PRG programming port add-on module. This MJ20-PRG module clicks in the PLC and provides one RJ11 socket for serial communications with a PC. This module is powered by the RS232 port from the connecting computer. Therefore the pin assignment is a little bit different from the default pin assignment on the RJ11 socket. The main difference is, that pin 1 and 6 on the RJ11 socket of the MJ20-PRG module are used as power supply. These pins have to be connected to handshaking outputs at the PC side on the RS232 port. Normally pin 7 (RTS) and pin 4 (DTR) are used on the DB9 connector.

Unitronics Jazz RJ11 RS232 programming cable

DB9	RJ11	Function
2	3	RxD		TxD
3	4	TxD		RxD
4	6	DTR		Power
5	2 + 5	Signal ground
7	1	RTS		Power

Omron PLC cables information

Omron PLC cable layouts

The PLC's from Omron can be connected to various peripheral equipment. Each device requires its own cable layout. Only the more common cables are shown here.

DB9 RS232 programming cable

DB25 RS232 programming cable

CV500-CIF01 toolbus programming cable

Mitsubishi PLC cables information

Mitsubishi PLC cable layouts

                Melsec PLC's from Mitsubishi can be connected to PC's running Medoc programming software using various cables. Each different I/O module uses a different pin assignment.

Not all Mitsubishi PLCs can be connected directly to a programming PC. The signal levels of the A series CPU units are not RS232 compatible and must be converted with a SC-02N or SC-05 converter. The serial cable layout to connect this converter to a PC is shown in this diagram.

PC to Mitsubishi SC-02N/SC-05 adapter cable

If more than one serial port is necessary on an A series melsec PLC, the AJ71C24 or AJ71C21 serial communication modules can be plugged into the system. These modules provide RS232 compatible serial ports, so no signal conversion is necessary to connect these modules with a PC. Both modules are equipped with a DB25 connector. The cable layout for these two modules is shown below.

PC to Mitsubishi AJ71C24 serial programming cable

PC to Mitsubishi AJ71C21 serial programming cable

The A1SJ71C24-R2 can also be used to connect computers and devices to a melsec series A PLC. This plug-in module contains two serial ports, each with a DB9 connector. The wiring layout is in fact identical to the RS232 null modem cable with loopback handshaking.

PC to Mitsubishi A1SJ71C24-R2 serial programming cable

 

Siemens PLC's

Most programming of Siemens S5 PLC's is done using a special RS232 to TTY converter. The S7 series are programmed using a RS232 to MPI bus converter. The easiest thing to do is buy these special cables from your local Siemens supplier. The operator terminals however can be programmed using a normal serial cable. The following cable can be used to program the OP series of operator displays.

Programming cable for OPxx display series

Idec / Izumi PLC's

Idec / Izumi PLC series FA2, FA2J and FA3J all require a special communication adaptor for programming. This communication link adaptor (CLA) is a small box that converts the RS232 electrical signals into a compatible level for the PLC. The cable to connect the PC to a CLA uses a DB25 connector at the PLC side. The layout for a cable with a DB9 connector at the PC side is shown here.

DB9 Programming cable for Idec / Izumi FA PLC series

Z-World microcontrollers

Z-World is an American company specialized in developing microcontroller boards based on the Z180 and Rabbit series micro controllers. Where PLC's are often used in single piece environments, micro controllers are mainly present in the OEM world where multiple controllers are needed.

The main difference in programming a PLC is that most microcontrollers, including those from Z-World, are programmed in C. The Z-World programming package runs on a normal PC and the connection with the controller is made using a serial cable. This cable needs a DB9 connector at one and, and a RJ14 plug at the other. The pin out of a programming cable is shown here.

DB9 Programming cable for Z-World PK microcontroller series