Diagram Cables

What is the definition of PLC wiring diagram?

A diagram that shows the locations that inputs and outputs are physically connected to PLC terminals. The physical locations do not directly affect the circuit logic.

PLC programming cables for several brands

Most PLC's can be programmed from a PC via a serial cable. Unfortunately, many of these cables have a non standard layout. De cables shown here can be bought from the regular sales channels, but it is often much cheaper to solder them yourself.

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.

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.

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.

List cables:

Hitachi PLC Cable Wiring Diagram

1. EH-150 port and cable connection [when using LADDER EDITOR for PC9801 (HL-PC3)]
<Cable: EH-RS05 + PCCB02H> - diagram1.pdf (397KB)

2. EH-150 port and cable connection [when using LADDER EDITOR for Windows® for PC9801]
<Cable: EH-RS05 + WPCB02H> - diagram2.pdf (531KB)

3. EH-150 port and cable connection [when using LADDER EDITOR (HL-AT3E) for AT compatibles]
<Cable: EH-VCB02> - diagram3.pdf (758KB)

4. EH-150 port and cable connection [when using LADDER DEITOR Windows® for AT compatibles]
<Cable: EH-RS05 + WVCB02H (for Windows®)> - diagram4.pdf (612KB)

5. EH-150 port and cable connection [when using GPCL01H] <Cable: EH-RS05 + GPCB02H> - diagram5.pdf (288KB)

6. EH-150 port and cable connection [when using a programmer] <Cable: EH-RS05 + PGCB02H> - diagram6.pdf (498KB)

7. EH-150 port and cable connection [when using the host] <Cable: EH-RS05 + Self-made cable> - diagram7.pdf (304KB)

Introduction to RS422

Serial communication methods to transfer information between equipment have been defined by standards for nearly half a century. The oldest and best known standard is RS232, a standard which defines the communication between DTE, data terminal equipment, and DCE, data communication equipment. The relatively short distances and low speed the RS232 serial interface can handle demanded for newer standards like RS422, RS423 and RS485. In this document, I will focus on the RS422 interface for serial balanced differential communications.

Differential balanced signals with RS422

Serial, balanced and differential are the keywords for the RS422 interface standard. Serial means, that the information is sent bit by bit on a single transmission line, just like with RS232. Balanced differential is what makes RS422 different from RS232. On RS232 interfaces, the signals are send on lines which share a common zero. With RS422, each signal line consists of two wires, preferably twisted to reduce noise. The voltage-difference between the two lines is an indication of the signal value, rather than the voltage-level. Looking at voltage differences with RS422 rather than levels eliminates a lot of noice induced by external sources and allows for higher data rates and cable lengths compated to RS232. You can see the differences in speed and cable length between RS422 and other commonly used serial interface standards like RS232, RS423 and RS485 in the interface comparison table.

Twisting the lines helps to reduce the noise. The noise currents induced by an external source are reversed in every twist. Instead of amplifying each other as in a straight line, the reversed noice currents reduce each others influence. The figure explains this in more detail.

Noise in straight and twisted pair cables
Noise in straight and twisted pair cables

Network topology with RS422

There are more differences between RS422 and RS232 than the maximum data speed and cable length. RS232 was specifically defined as an interface between computers, printers and terminals with modems. The modem would translate the communication signals to protocol usable for long distance communication, where long distance could also mean a device on the other side of the control room or building. RS422 allows the direct connection of intelligent devices, without the need of modems. Furthermore, where the RS232 linedriver is only designed to serve one receiver, a RS422 linedriver can serve upto ten receivers in parallel. This allows one central control unit to send commands in parallel to upto ten slave devices. Unfortunately, those slave devices cannot send information back over a shared interface line. RS422 allows a multi-drop network topology, rather than a multi-point network where all nodes are considered equal and every node has send and receive capabilities over the same line. If you need to build a multi-point communication network rather than multi-drop, RS485 is the right choice with a maximum of 32 parallel send and 32 receive units parallel on one communication channel. 

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.

Unitronics 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
Unitronics PLC RJ11 pin assignment

PinRS232 functionRS485 function
1DTRA (+)
2Signal groundRS232 signal
3TxDRS232 signal
4RxDRS232 signal
5Signal groundRS232 signal
6DSRB (–)

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
Unitronics RJ11 RS232 crossover cable

RJ11 plug 1RJ11 plug 2Function
25Signal ground
52Signal ground

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
Unitronics RJ11 RS485 cable

RJ11 plug 1RJ11 plug 2Function
11A (+)A (+)
66B (–)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
Unitronics RJ11 RS232 programming cable

52 + 5Signal ground

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
Unitronics Jazz RJ11 RS232 programming cable
52 + 5Signal ground