A pat on the back is only a few centimeters from a kick in the butt. - DILBERT

The Programmable Controller industry evolved in a way similar to the Personal Computer industry. At first, each vendor made all the components in their systems. Later, standard hardware components such as keyboards, power supplies, memory, and monitors evolved, as did vendors who specialized in these components. The component specialists became the lowest cost providers for their respective components, and soon anybody could build a system simply by selecting all the necessary components.

When PLC's were first available, promoters said a PLC was "simply a relay replacer". This indirect talk allowed PLC vendors to conceal the PLC's real substance - that it was a computer. PLC users have always been very concerned about reliability, and at this time the thought that a PLC was merely an industrial computer programmed in ladder logic would have scared them away. So, PLC promoters cleverly painted a different picture of PLC's, portraying them as a new form of mechanical relay, timer and counter.

In virtually no time at all, the PLC business thrived and users wanted more and more features. Soon PLC's could execute subroutines, solve complicated math expressions, and talk to each other over a cable.

Yet users were still being told that these PLC's were simply an advanced form of relay replacer. "Relay replacers that can execute subroutines, perform complicated math expressions, do PID, and talk among themselves over a cable..." Hardly sounds like a relay, does it?

The cable was not called a network, instead new words were coined to describe it such as: "Data Highway", "Modbus", and "Sy/Net". Everything but "network" was used. The hold on proprietary hardware solutions continued, even though there were better solutions available.

With time, users became familiar with computers. It was third party programming support vendors who made programming software available to run on standard IBM PC compatibles which drove the industry in this direction. The PLC suppliers wanted to keep their users entrenched in proprietary, dedicated, expensive programming terminals. This movement towards standard computers as a programming tool was something PLC suppliers fought tooth and nail.

Then finally when it was clear users would put up with nothing less, the PLC suppliers began to offer their own programming software on their own computers, a necessary business concession. The initial standard portable computers coming from the PLC vendors were as big as boats...

As time went on, users became very familiar with computers, DOS, programming languages, and networking, and most PLC users acquired computers for their homes as well. They developed a good understanding of what could be done with computers. They understood the simplicity of PC networking. They learned the technical language: RAM, ROM, firmware/BIOS, software, CPU...

Most importantly, they began to see PLC's as they really were: computers.

One day they realized:

PLC's were simply computers programmed to execute ladder logic! They were proprietary computers!

1. Proprietary, Closed Hardware Architecture. There was no hardware compatibility between PLC vendors. All spare parts had to come from the original vendor. The user was locked into his original vendor selection. There was no freedom to shop around based on price. PLC vendors would talk about open architecture but took little action. Just one example: vendors never took steps allowing the user to select one vendor's CPU to drive a competitor's I/O. When third party hardware support was available, its price was influenced by usually expensive technology licenses which had to be obtained from the proprietary PLC vendor.

2. Fixed Instruction Set. Applications often required industry-specific algorithms. Because of the proprietary, closed PLC architecture, there was no way to add new ladder instructions or use other languages without a special additional module or the help of the proprietary PLC vendor.

3. Slow Price/Performance evolution. Relative to the standard computer industry, the PLC industry's price/performance curve provided improvements to the user at a much slower rate. The proprietary PLC solutions were under less competitive pressure than those present in the personal computer industry. As a result, the personal computer industry was evolving at a much faster rate than the PLC industry. When improvements in PLC hardware price/performance did occur, they often came out as a new model bundled with an entirely new way of programming, thinking, training, and in general with little provision for a smooth migration to the newer PLC.

4. Weak Networking. Proprietary PLC's were limited in their ability to operate on standard computer networks. Usually proprietary PLC's were on one kind of network and computers were on another, often with special computers acting as a bridge or gateway joining the two kinds of networks. The proprietary PLC networks were far slower than the computer networks. There were a number of marginal improvements made by each proprietary PLC vendor in response to user complaints. Sometimes the speed improvements were clearly not worth the cost of introducing another type of network into the same facility. Eventually most proprietary PLC vendors added standard ethernet connectivity. Still, it was too little, too late. There were many other kinds of fast networks in the personal computer world that were not yet available to the PLC user: 100 MB FDDI, 100 MB ethernet, token ring, arcnet, and PCNET to name just a few.

About this time, a very creative company in Texas, called Tele-Denken, introduced what became known as SoftPLC. (Tele-Denken has since changed its name to SoftPLC Corporation.) SoftPLC was a software product which enabled the industry to build PLC's from standard computer and PLC hardware components. Users now had the flexibility to select hardware according to their priorities: reliability, features, cost, performance, or vendor relationships. And they could do it independently for CPU and I/O, on a component basis. SoftPLC was a liberating force for users of proprietary PLC's.

At the time of SoftPLC's introduction, SoftPLC Corp. had had over 10 years of experience as a PLC programming software vendor and was one of the major suppliers in this area. Its flagship product TOPDOC was known throughout the industry.

SoftPLC Corp.'s development of SoftPLC was evolutionary, having its roots in SoftWIRES, an Allen-Bradley PLC-5 emulation and simulation program first introduced back in 1986. The SoftWIRES technology was refined for over 6 years before being adapted for SoftPLC.

SoftPLC was used with the proven programming and support package, TOPDOC, giving it quality & maturity advantages over new software companies trying to enter the market of PC-based control.

SoftPLC enabled a large number of hardware vendors and systems integrators to become PLC providers. For the first time in PLC history, component specialists could now contribute their part to a totally open architecture PLC solution.

At first, proprietary PLC vendors became predominantly I/O vendors. Users often continued using whatever PLC I/O type they had been using but now with a standard CPU, one built from a standard industrial computer. Later some PLC vendors built CPU engines to run the SoftPLC software.

The ability to select from standard hardware components created increased competition and resulted in lower prices throughout the industry.

Users could now put their own PLC's on their normal everyday computer networks. SoftPLC could work on any TCP/IP compatible network, including intranets and the Internet. Both office computers and PLC's could now exist on the same network, if desired. Network support personnel could be shared across those environments. Spare parts were easier to come by.

SoftPLC overcame the four major disadvantages associated with proprietary PLC's:

1. Open Hardware Architecture. Nearly everybody could now be a PLC vendor. Users were no longer locked into their original hardware vendor selections. Price shopping was more predominant. As a convenience to their customers, SoftPLC also packaged their control software into standard industrial computers, known as SoftPLC Processors™.

2. Extensible Instruction Set. New application-specific ladder instructions could be developed by a C programmer. The new instructions would seamlessly integrate into the programming environment as if they were built in. The SoftPLC programming software, TOPDOC®, would automatically learn about the new instructions on the fly from SoftPLC. This was remarkably flexible and gave system integrators a real opportunity to contribute their application knowledge.

3. Blazingly Fast Price/Performance Evolution. The CPU component of the open architecture PLC (SoftPLC) was now simply a standard Intel86 computer. Users could upgrade their SoftPLC's whenever they wanted to invest in a more advanced CPU. The PLC industry's price/performance curve began to evolve under the exact same influences as the personal computer industry. When the quantum improvements in computer technology became available, such as the Pentium and Celeron CPU's, the price/performance benefits were immediately available to SoftPLC users. No new programming was necessary to make a hardware migration. The existing SoftPLC was simply loaded onto a new CPU and the existing I/O moved over. As new versions of SoftPLC became available it was easy to upgrade just by changing the software control kernel instead of rewiring and re-engineering.

4. Strong, Flexible Networking. SoftPLC's were added to existing proprietary PLC networks. More importantly, SoftPLC's were added to existing standard computer networks: ethernet, token ring, arcnet, PC NET, 100 MB FDDI, 100 MB ethernet. SoftPLC's could even be added to both proprietary PLC networks and standard computer networks simultaneously. The programming software, TOPDOC, could be run from any computer node on either kind of network to provide online run-mode programming and monitoring. Unlike proprietary PLC's, SoftPLC's could backup their own memory contents to disk and even to a file server.

About this time, there was a lot of talk about PLC programming languages other than ladder logic. Even so, ladder logic never went away for a number of good reasons:

Ladder could be modified while running. True run-mode online programming! It was graphical, and easier to quickly grasp what was going on than text based languages. A true control language! It was widely understood by plant floor electricians, the people who had to maintain the control software. Little if no training was required to move from proprietary to open architecture PLC's!

SoftPLC was initially conservative in its approach to alternate languages. Familiar ladder logic was used predominantly, but it could be used to call subroutines written in C, C++, or even the Java language, which were treated as new ladder logic instructions. Users used these custom functions for a wide variety of add-on capabilities -- from mathematical calculations or industry specific logic to custom communications to industrial devices, other computer applications, motion controllers, and more. Some users also used other language paradigms such as State Logic for their SoftPLC controllers.

e-Automation became an important part of successful Enterprise Control Systems, and SoftPLC led the way with the first embedded web server in a PLC. SoftPLC also added an embedded realtime Java Virtual Machine (JVM) which provided customers an easy, open-architecture interface between the realtime factory data in SoftPLC to other computer systems that performed database, accounting and other MIS/IT functions.

In the end, it turned out that proprietary programmable controllers were simply a proprietary form of industrial computer which served as a stepping stone between relays and conventional open architecture industrial computers.

Software such as SoftPLC has been a liberating force for PLC users!