Glossary of Terms
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ABG (Auto Bus Grant) Connector: A 96-pin DIN connector with the additional provision of automatic busing of VME daisy chain signals through empty card slots.
ANSI: The abbreviation for American National Standards Institute, which is the U.S. standards organization which participates in standards activities with the International Electrotechnical Committee (IEC).
Air Deflectors: Air deflectors are wedge shaped metal extrusions that can be secured to a card cage for the purpose of deflecting inlet air to areas of the card cage that are generally blocked by the extrusions that support the card guides.
Air Restriction: A system of metering plates that blocks airflow from empty slots within a card cage or enclosure and redirects it to hot function cards.
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Backplane: A two-sided or multilayer printed circuit board into which function cards can be plugged. The backplane transfers signals between the function cards. Mounted on the component side of the backplane are up to 21 connectors into which function cards can be plugged. On the solder side of the backplane are termination points (studs, Mate-N-Loks, power bugs, quick disconnects) for the distribution of power and ground.
BTL Transceiver: A bipolar device with a 1 volt swing conforming to IEEE 1194.1. BTL is an abbreviation for Backplane Transceiver Logic and is the specified technology for Futurebus+, profiles A, B, and F.
Bus: A circuit over which data or power is transmitted.
Bus Bars: Rigid conductive substrates for uninhibited distribution of power and ground. Tapped connections can be made at intervals along the bus bars to feed the power or distribute ground to the closest circuit requirement. Bus bars help reduce noise.
Bus Structure: A set of rules governing the circuit design of a system. There are many bus structures in the marketplace: VME, Multibus I, Multibus II, Versabus, Q-Bus, PC bus, Futurebus+, to name a few.
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Card Cage: A card cage or sub rack is a metal framework that supports function cards. The cage consists of metal endplates, extrusions, tapped strip, spacer strip, screws, flanges, and plastic card guides. There are two basic types of card cage design: rack mount and optional mount. The height of card cages is defined in units, i.e., 3U, 6U, 9U, 12U. One U is equal to 1.75 inches. The depth of card cages is measured in millimeters, i.e. 160mm, 220mm, 280mm, 400mm.
Card Cage/Backplane Assembly: A card cage with a backplane mounted in it.
Card Guide: A plastic or metal support for plug-in function boards. It relieves the stress on connector contacts, makes insertion into and extraction from the connector easier, and eliminates the possibility of twisting the board.
Card Mixing: Combining different size function cards in one card cage.
CFM: Cubic feet per minute.
CGS (Continuous Ground-Plane System): Provides a continuous, unified ground system for 2 or more modular backplanes.
Chassis Slides: Brackets mounted to the sides of an enclosure to allow it to slide in and out of an instrument rack.
Crosstalk: A false signal picked up by a signal line from an adjacent signal line caused by the electromagnetic coupling of adjacent conductors.
Custom Product: A product that is designed according to customer specifications.
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di/dt: The mathematical representation of the rate of change of current with respect to time. It is an important consideration when designing termination power delivery circuits.
Dielectric: Any insulating medium that intervenes between two conductors.
Daughter Board: Same as a function card or function board.
DIN: Deutsches Institut fur Normung is a German standards organization which has established many standards for the electronics industry.
DIN 41612: A standard governing a family of two part connectors on a .10 inch (2.54mm) grid used for connecting daughter cards to backplanes. The popular 3 row, 96 pin type C connector specified for VME and Multibus II is a member of this family of connectors.
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Eddy Current: A circulating current induced in a conductor caused by the electromagnetic field associated with a current in an adjacent conductor.
Edgecard Connector: A connection system in which the male contacts are etched onto the edge of a printed circuit board. This edge then plugs into a dielectric receptacle containing the female contacts. Multibus I uses this type of connector.
EMI/RFI: Electromagnetic interference/radio frequency interference.
Enclosure: A metal box designed to support function cards/transition cards, power supply, peripherals, cabling, fans, switches, for the operation of a bus system. Enclosures come in rack mount, desktop, and tower formats.
Endplate: Sheet metal that is cut to a specific shape or the end supports for the extrusions that make up a card cage.
Enhanced DIN Connector: Two rows of ground pins are added to the DIN connector to reduce ground bounce and connector crosstalk.
Extender Card: A board that plugs into the backplane in place of a function card. The function card is then plugged into the front of the extender card allowing the function card to extend out from the other cards for probe testing under live conditions.
Extrusion: A metal part made by forcing softened aluminum through a die to form the required shape and then cut to various sizes as needed. In card cages, extrusions make up the framework of the card cage.
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Flanges: Metal strips that have right angle extensions. They are attached to the end plates of a card cage to allow the cage to be mounted in a standard equipment rack. The protruding tab has mounting holes aligned to match rack mount requirements.
Flushmount: A card cage mounted flush with the front of the enclosure.
Function Card: A printed circuit board that plugs into a slot position of a backplane. Function cards can be custom designed by the user or bought as a standard off the shelf. A series of these cards can make up a system or sub-system to run machinery or many other electronic functions.
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Ground Plane: A common conductive surface that receives and returns power/signal transmissions.
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IEEE: The abbreviation for Institute of Electrical and Electronic Engineering which is the international professional organization for electrical engineers. It is an important standards producing body.
Impedance: The characteristic impedance of a transmission line is equal to the voltage divided by the current for a wave that is propagating along the transmission line, and is measured in ohms. This can apply to a single-ended signal line (transmission line characteristic impedance with respect to ground), or a signal pair (differential impedance). It is one of the important electrical characteristics of a backplane. It is determined by the physical dimensions of trace width, trace spacing, conductor thickness, dielectric thickness, dielectric constant, etc. Note that this is not the end-to-end resistance of the trace itself; rather, it is a characteristic of the transmission line environment .
Incident Wave Switching: New, faster technology which allows signals to be captured as they first pass each slot instead of waiting until they are reflected back to reach the usable threshold.
I/O Panel: A metal panel that is partially punched for mounting cable connectors for the transmission of data from one unit to another.
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Lateral Interconnect Board: Couples two modular VME backplanes together to form one continuous backplane.
LFM: Linear feet per minute.
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Microstrip: A backplane trace routing configuration in which a signal trace is positioned on the outer surface directly above a power or ground plane.
Modeling: A powerful tool that creates software equivalents which accurately represent the electrical characteristics of all the physical components of backplane systems.
Monolithic Backplane: Incorporates both the J1 and J2 backplanes on a single board with continuous power and ground planes.
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Optional Mount: A standard card cage without flanges that has end plates with mounting holes in four places for the ability of mounting in various positions.
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Peripherals: In Hybricon enclosures, peripherals refer to disk drives.
Powered Rack: A rack mount card cage with the addition of a power supply.
Propagation Delay: The time it takes for a signal to spread or distribute across an entire circuit.
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Rack Mount: A card cage or enclosure with flanges for mounting to a standard equipment rack.
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Signal: An electrical pulse which propagates across a backplane.
Signal Integrity: The characteristic of a signal path that allows a wave patter to pass undisturbed and undiminished from one point to another. This is an important aspect of all backplane and interconnect designs.
Simulation: The process of creating equivalent circuits with the models of components to perform electrical tests in a simulated mode.
Spacer Strip: A metal strip with equally spaced rectangular holes that slide into a slotted area of an extrusion. It is used to secure and accurately align card guides in a card cage.
Standard Product: A pre-designed product that is available off the shelf.
Static Pressure: In enclosures, impedances to the free flow of air create static pressure, which is measured in inches of water.
Stripline: A backplane trace routing configuration in which a signal trace is positioned between two ground or power planes. This layout style provides the greatest signal integrity.
Stub Length: The measured length of the signal trace.
Studs: Threaded posts that are mounted and soldered to specified points on a backplane. Each stud consists of a threaded post, threaded nuts, and washers. Power and ground wires are attached to these studs and to a power supply for powering up the backplane.
SU: A system unit defined in IEEE 1301 to be 25mm. Used as a basic dimension in hard metric packaging schemes.
Surface Mount: A method of mounting electronic components to a printed circuit in which components have flat pads which are soldered onto a pattern of pads on the circuit board. This technology is replacing thru hole methods of component mounting.
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Tapped Strip: A metal strip of equally spaced threaded holes that slide into the slotted area of an extrusion. It is used to secure a backplane to a card cage. Front panels are also secured in this manner.
Terminators/Inboard Terminators: A resistor network positioned at one or both ends of a signal path. Signals travelling along the bus arrive at its end or termination and will reflect from there or be dissipated. Terminators control the reflected signal. Inboard terminators are mounted on the backplane inside the outer connectors.
Thru Hole: A drilled hole in a circuit board that has been made conductive by the deposition of copper and the electroplating of an alloy layer of tin-lead. Such a conductive cylindrical hole wall forms an electrical pat to connect traces on inner and/or outer layers of a multilayer printed circuit board.
Trace: A conductive path on a printed circuit board usually formed by etching away much of the copper layer leaving a pattern of copper paths.
Transition Card: Similar to a function card but it plugs into the opposite side of the backplane. It allows different devices to communicate with each other.
Transmission Line: The electrical propagation characteristics of two adjacent signal paths is often compared mathematically to a transmission line (two adjacent parallel round conductors in free space). Such lines have distributed capacitance, distributed inductance and resistance.
TTL Transceivers: A tristate (totem pole) logic device for 5 volt digital interfaces. TTL is an abbreviation for Transistor to Transistor Logic and is the specified technology for VME and Multibus architectures.
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U: Unit of measurement equal to 1.75² .
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VME: An abbreviation for VERSA-Module Europe. An important 32 bit open computer architecture first developed in 1981 and based on the earlier VERSAbus architecture developed by Motorola.
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Wire Wrap Board: A circuit board that is manufactured to the physical dimensions of a function card that conforms to a bus specification. It is also called a prototype board because a user can plug in circuit packages and hand wire a circuit for actual use.
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