The history of industrial I/O buses: S-100, ISA, PC104, VERSAbus, and VMEbus.

Introduction

The automation of an industrial system has evolved significantly, but its strength has largely remained based on PLC (Programmable Logic Controller) architectures, primarily used in large industrial plants.

The most well-known manufacturers of electrical and electronic components have developed increasingly powerful PLC lines.

However, using a PLC in certain control applications where operator interface (HMI) support, connectivity, and—ideally—multiprocessing are required is often difficult, if not impossible.

As a result, industrial control systems based on boards with various interconnection methods have often been used and continue to be utilized today.

Below, we highlight the most significant ones.

The Origins

The first semi-industrial interconnection system was the "S-100" bus. It was a passive backplane with 100-pin connectors and was used to host a CPU board (typically based on the Motorola 68020 microprocessor) in one slot, while other slots accommodated expansion boards with various I/O functions.

This was back in 1974.

From there, various types of interconnection systems ("buses") were developed. The philosophy is primarily based on a backplane with connectors that host a CPU board (or multiple CPUs) and several I/O and memory expansion boards.

At this point, however, it's essential to distinguish between the two "worlds" used for industrial applications: the "PC-based world" and the "world based on industrial boards with microprocessors/microcontrollers."

The PC World

ISA BUS
With the use of PCs in industrial environments, there has been a widespread use of so-called "add-on" boards to manage I/O functions toward the process.

The interconnection system was the well-known "ISA" ("Industry Standard Architecture"), which had very limited performance but was adequate for the old Intel processors from over 30 years ago.

"ISA" is a parallel bus that supports 8/16-bit data.

PC104 BUS
When there was a desire to provide a more reliable and industrial form factor for the ISA bus, square-shaped boards with pin connections emerged. The PC104 format allowed (and still allows) for the creation of "stacks" of boards stacked on top of one another, sharing the common ISA bus.

PCI BUS
With the evolution of x86 processors, the bus evolved into the PCI bus. Still parallel, it became very popular, and PCI add-on boards are still widespread. The PCI BUS has significantly higher performance than the old ISA, allowing for 32-bit data flows.

PC104+ BUS
With the advent of the PCI bus, the PC104 board format evolved, adding an additional stackable connector. The new boards were named "PC104+".

PCI Express
Now, many systems based on PC architectures use the new interconnection bus "PCI Express (PCIe)," which consists of various high-speed serial lines (from 1 to 16 lines, called "lanes"). When engineering a PC, especially if it's in a "boxed" format to accommodate various I/O boards, it is preferable to use PCIe expansion.

The World of Microcontroller Boards

To achieve greater I/O flexibility and enhanced robustness in control systems, various interconnection systems have gained significant popularity.

VERSAbus

The VERSAbus was a system bus architecture used in the PDP-11 series minicomputers developed by Digital Equipment Corporation (DEC) in the 1970s. This bus allowed communication between the CPU, memory, and various peripheral devices within the system, using an asynchronous topology to facilitate modular expansion and integration of new interface boards.

The VERSAbus architecture supported 16-bit data transfer, with a dedicated signal set for managing memory access and interrupt control, enabling flexible configuration and interconnection of heterogeneous hardware components within the same system.

VMEbus

The most famous is undoubtedly the VME bus ("Versa Module Eurocard").

Originating from Motorola, it has been used in challenging industrial environments as well as in military applications.

The most well-known CPU board was the “MVME162” (Motorola), which is still highly sought after as spare parts in strategic applications: controlling reactors in chemical and petrochemical plants, rolling mills, naval applications, etc., where it is preferable to find a refurbished but fully functional board, even at a high price, rather than spend enormous amounts to redo the entire control system of the plant.

What CJB has to offer

Over the years, CJB has specialized in supporting VME spare parts and the spare parts for certain functional boards with PCI, ISA, and PC104(+) buses.

If you need to integrate a current or legacy bus technology into your industrial systems, or if you require spare parts, refurbished boards, or need to perform reverse engineering of a protocol or non-standard communication bus, please contact us for more information.