Esd electronics develops VME components that replace both its own assemblies and discontinued third-party products. In the same year that the first CD player was launched, Motorola, Mostek, Philips/Signetics and Thomson presented the VMEbus at the Systems trade fair in Munich. This was in 1981 and was the first license-free and open bus system for industrial and scientific applications. This open and flexible system architecture promised many advantages. Even today, computer systems that use the VMEbus are still used in projects such as the International Space Station (ISS) or in the European navigation system Galileo, but also in industrial control technology projects, in the maritime environment, in medical technology and in military/aerospace applications.

The origins

VME stands for VERSAmodule Eurocard and describes the backplane bus of a computer. The name VMEbus was derived from this - the term VERSAbus is now rarely used. The VME bus system is a modular and robust system architecture in a 19" rack with modules in double or single Eurocard format and gas-tight DIN connectors. It was developed as a multi-master bus system in the early 1980s for the Motorola 68000 processor family. A few years later, the IEC standardized the system in ANSI/IEEE 1014-1987 with the following key features, which were expanded over time:

• Master/slave architecture with the option of multi-master operation
• Asynchronous bus, later expanded to include synchronous data traffic
• Arbitration methods for bus allocation
• Address width between 16, 32 bit and 64 bit
• Data path width between 8 and 32 bits and up to 64 bits in current systems
• Bandwidth up to 40 Mbyte/s, in newer versions also up to 320 Mbyte/s
• Interrupts with up to seven priorities, daisychain and interrupt vectors
• Up to 21 plug-in cards can be contacted via one backplane

It is said that technology moves fast, but the VMEbus system has always been able to assert itself against competitors such as Q-Bus, Unibus and Multibus I and II.

Know-how in theory and practice

esd electronics recognized the advantages of the VMEbus system at an early stage and developed its own industrial-grade computers and boards. Accordingly, the company now has more than 30 years of experience in the development of such systems and is a member of the VMEbus International Trading Association VITA. The VMEbus continues to impress with

• Independence from the microprocessor
• Use of a reliable mechanical standard
• Simple increase of the data width to 32 bit and 64 bit possible
• License-free and freely available specification
• Manufacture of compatible products by various independent suppliers
• Plug-in cards with different clock rates can be used without clock reduction
• Cost-effective system expansions
• Single-stage interrupt structure for deterministic real-time operation

A particular strength of esd electronics is the development of VMEbus boards according to customer-specific requirements for individual applications. This includes replacement components for discontinued own products as well as for modules from other manufacturers. With these, systems designed for the long term can continue to operate reliably without complex validation processes. Here are a few examples.

Further developed SIL-compliant control system

Stage technology systems are located in direct proximity to stagehands and actors, who have to rely blindly on the technology. Safety standards are there to protect people, but also to maintain feasible systems. Theatertechnische Systeme TTS from Syke plans and implements stage technology systems. At the end of the 1990s, the company worked with esd electronics to develop a control concept in accordance with SIL (Safety Integrity Level) based on VMEbus computers. A concept that is still state of the art today. The control concept is based on a dual VMEbus master computer and axis computers connected to it, which control the drives. In order to meet the new requirements, CPU cards with a more powerful computer architecture were developed. These newly developed CPU cards with PowerPCs and Ethernet ports now exchange their data via Ethernet instead of CAN as before. Customer-specific changes such as these show how replacement cards bring existing VMEbus systems up to the technically required standard.

Evaluation of interferometers

Interferometers are used to measure very small changes in length. The principle used here is to send light through a beam splitter on two different paths through the instrument. The slightest changes in the light paths lead to a change in the interference pattern. Laser interferometers are used, for example, to determine the surface quality of lenses, mirrors or metallic bodies with maximum accuracy. Among other things, the position of the laser must be determined when evaluating the interferometer. To do this, the interferometer transmits signals via the VMEbus to the control computer, which uses them to determine the position of the laser. Carl Zeiss has been using the VMEbus computer VME-CPU/T10 and the XMC-CPU/T10 from esd electronics as control computers for around six years. The systems are constantly being further developed due to ever-increasing requirements, resulting in the high-performance systems of today.

Control and monitoring of systems

VMEbus systems for control and monitoring have proven themselves in production plants in the pharmaceutical industry. Due to component discontinuations, esd electronics developed a VME control computer and VME I/O boards. In this replacement development, the firmware was adapted so that the customer could replace the new boards without further system intervention and continue to produce and sell the system in the same way. With the VME-CPU/T10 control computer and the VME-DIO32 I/O boards, the customer received components with new hardware and firmware with the same functionality. This simplifies replacement and offers long-term availability again.

Test systems aircraft construction

The author: Hans Kürsten is Head of Product Management at esd electronics.

© esd electronics

Airbus Defence&Space has been building VMEbus-based test systems for more than 20 years to check the complex functions of an aircraft during maintenance. The VME-PMC-Caddy/2 carrier board is equipped with the XMC-CPU/2041 mezzanine card, which is currently being replaced with the Xilinx Zynq Ultrascale+-based XMC-CPU/Zulu. The combination is used to connect industry-relevant bus systems and protocols to the existing test system as well as for data acquisition and data pre-processing. Airbus benefits from the concept as the mezzanine cards can be modernized step-by-step while the system remains largely unchanged. This allows the company to use its development resources efficiently.