The STEbus is a non-proprietary, processor-independent, 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.
It remains a well-designed standard. Although no longer competitive in its original market, it could be a valid choice for hobbyists wishing to make 'home brew' computer systems. The Z80 and probably the CMOS 65C02 would be good processors to use. The standardised bus would allow hobbyists to interface to each others designs.
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 busis based on Intel 8080signals, the STDbusaround Z80signals, and the G64bus around 68000signals.
This made it harder to interface other processors. Upgrading to a more powerful processor would subtly change the timings, and timing restraints 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.
VMEbushad provided a high-quality solution for high-performance 16-bit processors, using reliable DIN41612 connectors and well-specified Eurocardboard 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
VMEbussimplified 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 Eurocardbut allowed for double-height boards as well. The latter positioned the bus connector so that it could neatly merge into VME-bus systems.
The STEbus was very successful in its day. It was given the official standard
IEEE1000-1987, and supported processors from the popular Z80, the 6809, to the powerful 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.
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.
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.
Moving on, PC systems did away with the need for card cages and backplanes by moving to the
PC104format where boards stack onto each other. While not as well designed as the STEbus, PC104 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.
The IEEE have withdrawn the standard, not because of any faults but because it is no longer active enough to update.
DIN41612, rows a and c, 0.1" pitch.
Eurocard- The most common size was the 100 x 160 mm Eurocard.
Eurocard- Rare, sometimes used in VMEbus hybrid boards
* [http://www.howell1964.freeserve.co.uk/Arcom/STEbus.htm STEbus connector and signal description]
* [http://www.howell1964.freeserve.co.uk/Arcom/ArcomManuals.htm STEbus boards and manuals]
* [http://standards.ieee.org/reading/ieee/std/busarch/1000-1987.pdf STEbus (IEEE1000) standard (requires payment)]
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