VMEbus: Highly stable in demanding projects
Due to its robustness and real-time capability, the standardized VMEbus technology is still used today in projects with greater demands. To ensure future availability esd electronics develops VME components replacing both its own assemblies as well as those of discontinued third-party products.
In the same year, when the first CD player was launched, the companies Motorola, Mostek, Philips/Signetics and Thomson presented the VMEbus at the trade fair Systems in Munich. That was back in 1981. In those days it was the first license-free and open bus system for industrial and scientific applications. This open and flexible system architecture held out the prospect of many advantages. Even today, computer systems based on the VMEbus technology are used in highly regarded projects such as the International Space Station (ISS) or the European navigation system Galileo. It is also found in projects of industrial control technology as well as in the maritime environment, in medical technology and in military/aerospace applications.
VME stands for VERSAmodule Eurocard and depicts the backplane bus of a computer. That is where the name VMEbus is derived from – the term VERSAbus is rarely used anymore.
The VMEbus system is a modular and robust system architecture in a 19 inch rack. It includes modules in double or single Eurocard format and gas-tight DIN connectors. As a multi-master bus system, it was developed in the early 80s for the Motorola processor family 68000. A few years later, the IEC defined the standard ANSI/IEEE 1014-1987 for the system which included the following essential features having been extended over the years:
- Master/slave architecture with the possibility of multi-master operation
- Asynchronous bus, later extended to include synchronous traffic
- Arbitration methods for bus allocation
- Address width between 16, 32 bits and 64 bits
- Data path width between 8 and 32 bits and in current systems up to 64 bits
- Bandwidth up to 40 Mbyte/s, in newer versions also up to 320 Mbyte/s
- Interrupts with up to seven priorities, daisy chain and interrupt vectors
- Up to 21 plug-in cards can be connected via a backplane
Even though technology is fast-moving, the VMEbus system was able to survive against some hard competition, for example from the Q-Bus, Unibus as well as from Multibus I and II.
VMEbus: Highly stable in demanding projects Full technical report on VMEbus: Highly stable in demanding projects (PDF) 2 MB
Despite its respectable age, the VMEbus system is still in use in many projects today. Discontinued components for this system do not necessarily have to herald a system change. Compatible replacement products can be implemented and are accompanied by the know-how and experience from esd electronics. The company is careful to ensure that hardware and firmware as well as functions remain compatible, which greatly simplifies the replacement of assemblies. A recent example of this is the VME-DIO32. With the help of compatible replacement components for esd own products as well as for products from other manufacturers, the VMEbus system remains state-of-the-art without the customer having to decide for an alternative technology. This can drastically reduce the development and validation effort.