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VMEbus is a computer bus standard originally developed for the Motorola 68000 line of CPUs, but later widely used for many applications and standardized by the IEC as ANSI/IEEE 1014-1987. It is physically based on the Eurocard sizes, mechanicals and connectors, but uses its own signalling system, which Eurocard does not define. It was first developed in 1981, and continues to see widespread use today. In computer architecture, a bus is a subsystem that transfers data or power between computer components inside a computer or between computers. ...
The Motorola 68000 is a 32 bit CISC microprocessor, the first member of a successful family of microprocessors from Motorola, which were all mostly software compatible. ...
CPU redirects here. ...
The initials IEC can stand for: Independent Electoral Commission Industrial Emergency Council Inertial electrostatic confinement (in fusion energy) Institut des Experts-comptables et des Conseils fiscaux Institut dEstudis Catalans, Catalan Studies Institute Interactive Evolutionary Computation International Education Centre International Electrical Congress International Electrotechnical Commission See also IEC connector for...
The American National Standards Institute (ANSI) is a private, non-profit standards organization that produces industrial standards in the United States. ...
The Institute of Electrical and Electronics Engineers or IEEE (pronounced as eye-triple-ee) is an international non-profit, professional organization incorporated in the State of New York, United States. ...
Eurocard is a European standard format for PCB cards, which can be plugged together into a standardized subrack. ...
History
In 1979 Motorola were developing their new 68000 CPU, and one of their engineers, Jack Kister, decided to set about creating a standardized bus system for 68000-based systems, which he called VERSAbus. He was later joined by John Black, who refined the specifications and created the VERSAmodule product concept. Sven Rau and Max Loesel of Motorola-Europe added a mechanical specification to the system, basing it on the Eurocard standard that was then late in the standardization process. The result was first known as VERSAbus-E, but was later renamed to VMEbus, for VERSAmodule Eurocard bus (although some refer to it as Versa Module Europa). Motorola (NYSE: MOT) is an international communications company based in Schaumburg, Illinois, a Chicago suburb. ...
Jack Kister (born 1951) is an engineer who worked on the TTL model for the original 68000 microprocessor at Motorola. ...
Eurocard is a European standard format for PCB cards, which can be plugged together into a standardized subrack. ...
At this point a number of other companies involved in the 68000's ecosystem agreed to use the standard, including Signetics, Philips, Thompson, and Mostek, and soon it was officially standardized by the IEC as the IEC 821 VMEbus and by ANSI and IEEE as the ANSI/IEEE 1014-1987. The initials IEC can stand for: Independent Electoral Commission Industrial Emergency Council Inertial electrostatic confinement (in fusion energy) Institut des Experts-comptables et des Conseils fiscaux Institut dEstudis Catalans, Catalan Studies Institute Interactive Evolutionary Computation International Education Centre International Electrical Congress International Electrotechnical Commission See also IEC connector for...
The original standard was a 16-bit bus, designed to fit within the existing Eurocard DIN connectors. However there have been several updates to the system to allow wide bus widths, and the current VME64 includes a full 64-bit bus in a 6U sized card, and 32-bit for 3U cards. The VME64 protocol has a typical performance of 40 MByte/s. Other associated standards have added hot swapping (plug-and-play) in VME64x, smaller cards known as IP's that plug into a single VMEbus card, and various interconnect standards for linking VME systems together. In computer science, 16-bit is an adjective used to describe integers that are at most two bytes wide, or to describe CPU architectures based on registers, address buses, or data buses of that size. ...
Deutsches Institut für Normung e. ...
In computing, a 64-bit component is one in which data are processed or stored in 64-bit units (words). ...
32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ...
Plug and Play is a term used in the computer field to describe a computers ability to have new devices, normally peripherals, added to it without having to restart the computer. ...
VMEbus was also used to develop a closely related standard, VXIbus. The VXI bus architecture is an open standard platform for automated test based upon VMEbus. ...
Description In many ways the VMEbus is the pins of the 68000 run out onto a backplane. In most cases this is a bad design, because it limits you to systems similar to the chipset the bus was originally designed for. However one of the key features of the 68000 was a flat 32-bit memory model, free of memory segmentation and other "anti-features". The result is that while VME is very 68000-like, the 68000 is generic enough to make this a non-issue in most cases. A backplane is a circuit board (usually a printed circuit board) that connects several connectors in parallel to each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus. ...
32-bit is a term applied to processors, and computer architectures which manipulate the address and data in 32-bit chunks. ...
On the Intel x86 architecture, a memory segment is the portion of memory which may be addressed by a single index register without changing a 16-bit segment selector. ...
Like the 68000, VME uses separate data and address buses, both 32-bits. In the case of the 68000 the address bus was actually 24-bits and the data bus 16-bits (although it was 32/32 internally), but the designers were already looking towards full 32-bit implementations. In order to allow both widths of buses to be used, VME uses two different Eurocard connectors, the P1 and P2. P1 contains three rows of 32 pins each, implementing the first 24-bits of the address and 16-bits of the data buses, along with all of the control signals. The P2 contains one more row, which includes the remaining 8 address and 16 data pins.
In order to control the bus a set of nine lines known as the arbitration bus is used. All communications are controlled by the card inserted in slot one of the Eurocard chassis, known as the arbiter module. In general use the cards will request access to the bus by holding the bus request in lines of the arbitration bus low to indicate their slot number. When the arbiter module frees the bus it scans these lines to see if there are any held low. If so, it pulls the bus busy line low to indicate the bus is going busy again, and writes the card number back out on the bus grant out lines.
At this point the numbered card has gained access to the bus. To write data the card writes the address and data to the bus, and then pulls the address strobe line and the two data strobe lines low to indicate the data is ready, and then pulls the write pin to indicate the operation. There are two data strobes so the cards can indicate if the data is 8, 16, or 32 bits (or 64 in VME64). The card at the indicated address on the bus then reads the data and pulls the data transfer acknowledge line when it is complete (or the bus error line if need be). Reading data is essentially the same, but the controlling card places only the address on the bus and pulls the READ pin. The other card then writes the data and pulls the data strobe pins when the data is ready. This signalling scheme is asynchronous, meaning that there is no overall clock signal as there is in synchronous buses such as PCI. 32-bit PCI expansion slots on a motherboard 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ...
VME also includes an interrupt bus, supplying all seven of the 68000's interrupt pins. When an interrupt is supplied the arbiter module writes the interrupt level back out to the address bus to tell which interrupt is being handled. Note that there is no concept of card number in this case, because cards will often share interrupts. The excessive number of interrupt levels has often been pointed to as one of the few examples of overdesign in the 68000, and it makes even less sense in the case of a bus.
Note that in VME all transfers are DMA and every card is a master (or slave). In most bus standards there is a considerable amount of complexity added in order to support various transfer types and master/slave selection. For instance, in the ISA bus both of these features had to be added on top of the already existing "channels" model where all communications was handled by the host CPU. This makes VME considerably simpler at a conceptual level while being more powerful, although it requires somewhat more complex controllers on each card in order to work. Direct memory access (DMA) allows certain hardware subsystems within a computer to access system memory for reading and/or writing independently of the CPU. Many hardware systems use DMA including disk drive controllers, graphics cards, network cards, and sound cards. ...
Industry Standard Architecture (in practice almost always shortened to ISA) is a bus standard for IBM compatibles introduced in 1984 that extends the XT bus architecture to 16 bits. ...
CPU redirects here. ...
In its later years, VME was used for all kind of CPU designs, including VME boards with HP PA-RISC, Motorola 88000 and PowerPC processors. PA-RISC is a microprocessor architecture developed by Hewlett-Packards Systems & VLSI Technology Operation. ...
The 88000 (m88k for short) is a microprocessor design produced by Motorola. ...
PowerPC is a RISC microprocessor architecture created by the 1991 Apple-IBM-Motorola alliance, known as AIM. Originally intended for personal computers, PowerPC CPUs have since become popular embedded and high-performance processors as well. ...
See also Data acquisition is the sampling of the real world to generate data that can be manipulated by a computer. ...
Camac Harps (Les Harpes Camac) is a French company that manufactures pedal (concert) harps, lever (folk) harps, and electric pedal and lever harps. ...
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