The STEbus (also called the IEEE-1000 bus) is a non-proprietary, processor-independent, computer bus with 8 data lines and 20 address lines. It was popular for industrial control systems in the late 1980s and early 1990s before the ubiquitous IBM PC dominated this market. STE stands for STandard Eurocard. Although no longer competitive in its original market, it is a valid choice for hobbyists wishing to make 'home brew' computer systems. The Z80 and probably the CMOS 65C02 are possible processors to use. The standardized bus allows hobbyists to interface to each other's designs.
Origins
In the early 1980s, there were many proprietary bus systems, each with its own strengths and weaknesses. Most had grown in an ad-hoc manner, typically around a particular microprocessor. The S-100 bus is based on Intel 8080 signals, the STD Bus around Z80 signals, the SS-50 bus around the Motorola 6800, and the G64 bus around 6809 signals. This made it harder to interface other processors. Upgrading to a more powerful processor would subtly change the timings, and timing constraints were not always tightly specified. Nor were electrical parameters and physical dimensions. They usually used edge-connectors for the bus, which were vulnerable to dirt and vibration. The VMEbus had provided a high-quality solution for high-performance 16-bit processors, using reliable DIN 41612 connectors and well-specified Eurocard board sizes and rack systems. However, these were too costly where an application only needed a modest 8-bit processor. In the mid 1980s, the STEbus standard addressed these issues by specifying what is rather like a VMEbus simplified for 8-bit processors. The bus signals are sufficiently generic so that they are easy for 8-bit processors to interface with. The board size was usually a single-height Eurocard (100 mm x 160 mm) but allowed for double-height boards (233 x 160 mm) as well. The latter positioned the bus connector so that it could neatly merge into VME-bus systems. IEEE Working Group P1000 initially considered simply repinning the STD Bus, replacing its card edge connector with the DIN41612 connector. But they decided to create a completely new high-performance 8-bit bus. They decided to make a bus more like the VMEbus and Futurebus. The STEbus was designed to be manufacturer independent, processor independent, and have multimaster capability.
Maturity The STEbus was very successful in its day. It was given the official standard IEEE1000-1987. Many processors were available on STEbus cards, across a range of price and performance. These boards included the Intel 8031, 8085, 8088, 80188; the National Semiconductor 32008 and 32016; the Motorola 6809, 68000, and 68008; The Zilog Z80 and Z280; the Hitachi HD64180; and the Inmos Transputer. The STEbus is designed for 8-bit microprocessors. Processors that normally use a wider data bus (16-bit, etc.) can use the STEbus if the processor can handle data in byte-wide chunks, giving the slave as long as it needs to respond. The STEbus supported processors from the popular Z80, the 6809, to the 68020. The only popular micro notably absent was the 6502, because it did not naturally support wait-states while writing. The CMOS 65C02 did not have this shortcoming, but this was rarer and more expensive than the NMOS 6502 and Z80. The 6809 used cycle stretching. Peripheral boards included prototyping boards, disc controllers, video cards, serial I/O, analogue and digital I/O. The STEbus achieved its goal of providing a rack-mounting system robust enough for industrial use, with easily interchangeable boards and processor independence. Researchers describe STEbus systems as rugged, adaptable, and cost effective.
Decline The STEbus market began to decline as the IBM PC made progress into industrial control systems. Customers opted for PC-based products as the software base was larger and cheaper. More programmers were familiar with the PC and did not have to learn new systems. Memory costs fell, so there was less reason to have bus-based memory expansion when one could have plenty on the processor board. So despite the disadvantages, manufacturers created industrial PC systems and eventually dropped other bus systems. As time went on, PC systems did away with the need for card cages and backplanes by moving to the PC/104 format where boards stack onto each other. While not as well-designed as the STEbus, PC/104 is good enough for many applications. The major manufacturers from its peak period now support STEbus mostly for goodwill with old customers who bought a lot of product from them. As of 2013, some manufacturers still support STEbus, G64, Multibus II, and other legacy bussed systems. The IEEE have withdrawn the standard, not because of any faults but because it is no longer active enough to update.
Physical format 3U Eurocard - The most common size was the 100 x 160 mm Eurocard. 6U Eurocard - Rare, sometimes used in VMEbus hybrid boards
Connector DIN 41612, rows a and c, 0.1" pitch. VME/STE hybrid boards have the STEbus and VMEbus sharing the VME P2 connector, VME signals on row b. For this reason, STEbus boards may not use row b for any purpose.
Pinout
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