Welcome to Heinz Page for Industrial Programming.

This page provides an overview and internet resources for developing embedded applications for reliability, portability, vendor independence, distributed computing and interoperability. The page is still under construction.

Open PLC IEC-1131-3 programming on standard hardware with a realtime operating system.

Today a lot of embedded software is developed in C without an operating system, A low cost hardware platform such as PC/104 can be much better utilised with a proper operating system than with DOS or without operating system. PLC type programs are very well suited for analog/digital inputs/outputs, sequences, control and other routine tasks. Many PLC languages are awkward and not well suited for "general purpose" programming. The IEC-1131-3 is a standard for programming PLC functionality. As well as targeting standard PLC hardware it can be run on standard personal computers or industrial computers. With a suitable operating system you can run one or several PLC-programs at the same time as you run other tasks in parallell. The PLC-programs manages analog/digital I/O, sequences, control functions etc. A separate task handles communication over network or fieldbus. Still other tasks for operator interaction, computation, data logging and presentation can be run in parallell.

IEC-1131-3 Open PLC software development standard:

The IEC-1131-3 specifies 5 languages for PLC programming.

Graphical Languages:

Sequential Function Chart (SFC) Which is based on Grafcet which is a separate IEC standard (IEC-848).
Ladder Diagram (LD)
Function Block Diagram (/FBD)

Textual Languages:

Instruction List (IL)
Structured Text (ST).

The IEC-1131-3 promises:

Integrated development systems for PLC programming, with graphical program representation, hosted on standard platforms such as Microsoft Windows.
Portability of source code over a wide range of hardware: PLCs, Micro Controllers, Industrial Computers, Personal Computers
Integration of specification, program development and system documentation
Component and system testing in the development environment
Modularised support for different fieldbus protocols via a single real time data base of PLC variables

There are several independent IEC 1131-3 products available. For example:

Paradym-31

Wizdom Controls

ISaGRAF by CJ International

Other IEC-1131-3 related links:

PLCOpen

IEC-1131-3 Documents

Articles on IEC-1131-3

Critique

An attempt to create a standard language for can be claimed to be counterproductive .

Object orientation ideas are not incorporated in the standard. This makes it harder to incorporate in a OO development process where the analysis and design phases should be easily mapped on to the language. Some interesting object oriented analysis and design links:

Shlaer-Mellor

Unified Modeling Language

ROOM

For plant engineering and large scale automation there are very well designed PLC/DCS/OCS solutions which are not yet much affected by the "standard". Two good examples are ABB Advant OCS and Siemens Simatic

When you evaluate a IEC-1131 package you should be extra careful to examine what ready to use function blocks exist. This can very well make the difference between a complete language and a complete PLC solution.

Industrial Computing, SCADA, Real Time Computing and Operating Systems, Embedded systems:

Embedded Systems Internet Resources

Scada Sources and Real Time References

Real time operating systems suited in this context:

OS-9 at Microware

OS-9 Frequently Asked Questions

QNX

A few things a real time operating should offer:

Process management and scheduling.
Memory management
Interprocess communication
Predictive response times to external events
Interrupt handeling and hardware driver support
Scalability
Unix/POSIX conforming programming model
Networking support (TCP/IP)

Standard Hardware Platforms/Buses:

PC/104

Pep Modular Computers

Fieldbuses:

A standard fieldbus promises real distributed control in industrial computing.

Fieldbus communication, (in general):

Low cost
Taylored to industrial environments for reliablity and predictability
Much richer information transfer capabilities compared to 4-20 mA transmitters
Good real time characteristics
Interoperability between devices from several vendors

Fieldbus resources:

Field Bus Home Page

PROFIBUS International

Steinhoff offers interesting hw/sw products for IEC-1131 and fieldbuses based on QNX rtos.

Networking:

TCP/IP

Sockets

Modern well designed general purpose programming languages

C++ is without doubt the most used object oriented language. Regardless of its strengths and weaknesses it is not well designed. See Ian Joiners C++ critique . It is quite clear that a modern general purpose language must have the necessary elements for object orientation. Usually Encapsulation, Inheritance and Polymorphism, are stated. For application programming it is clear that automatic memory management ( no explicit pointer variables, garbage collection) should be added to the list. Object orientation can be elegantly implemented without leaving the the Algol, Simula, Pascal, Ada tradition. A well designed type system, strict compile time type checking, clear syntax and orthogonality are very important software engineering issues. Don't forget that Simula was the first object oriented language and that it is still modern after 30 years.

I have used Modula-2 a lot. It also comes in OO flavours. Its successor Oberon-2 is my favourite. Ada-95 has got everything that Ada-83 has and also qualifies as an object oriented language. Both Oberon-2 and Ada-95 use the type extension concept rather than the class concept. In principal both acheives the same goals but there are differences.

Don't forget to investigate Eiffel if you are looking for a language suited for large projects. Eiffel has a good and versatile standard library and is very well thought out in every OO detail.

Java borrows its syntax from C and a lot of object orientation philosophy from Smalltalk. But Java also has elements from the above languages. It could very well be a very good alternative in the embedded/real time arena in the future.

Any comments to the content and validity of the information on this page are welcome. If you are a vendor of a related product please supply me with information or a web address and I will include it on this page. (If I think it is relevant).

Other comments and questions are welcome by email

Heinz Ericson <heinz@lysator.liu.se>