Backplanes

Backplanes are circuit boards that contain sockets or expansion slots for connections to other circuit boards. There are two types of  backplanes: active and passive. Active backplanes contain bus control and motherboard circuitry; however, they do not contain processor complex components such as the central processing unit (CPU), chipset, or cache. Passive backplanes contain circuitry for bus connectors and, in some cases, buses and drivers. Buses are devices that transmit data from one part of a computer to another. Drivers interface hardware devices to an operating system or other software. Both active and passive industrial backplanes may also include bridges that interface two buses of the same type or of different types. 

Backplanes use many types of buses. Industry standard architecture (ISA) buses are I/O devices that can handle 16-bit data transfers at a clock speed of 8 MHz. Extended ISA (EISA), an enhanced version of the ISA bus, is capable of 32-bit data transfers. Peripheral component interconnect (PCI), a local bus system for high-end computers, can transfer 32 or 64 bits of data at a clock speed of 33 MHz.  Compact PCI (cPCI) uses the electrical standards of the PCI bus, but is packaged in a Versa Module Eurocard (VME) bus. The VME bus (VMEbus) is a rugged, 32-bit device used in industrial, commercial and military applications. VME64 is an expanded version of the VMEbus that provides 64-bit data transfers. VME64 extended (VME64x) adds a 160-pin connector, 3.3 V power supply pins, bandwidths up to 160 MBps, and hot swap capability. VME320 is a modified VMEbus that transmits data synchronously and features a bandwidth range from 320 MBps to over 500 MBps. VME160 is the 160 MBps version of the VME320 standard. Other bus types include VME extensions for instrumentation (VXI), multisystem extension interface (MXI), embedded technology extended (ETX), and embedded PCI extended (ePCI-X). Advanced telecommunication computing architecture (AdvancedTCA) is an open specification for carrier grade equipment. Host media processing (HMP) performs the media processing functions of communications applications without special-purpose telephony hardware.

There are many form factors for backplanes. Advanced technology (AT) is the original IBM motherboard design for personal computers (PCs). Full-size AT boards are up to 12” wide by 13.8” deep. By contrast, small or “baby” AT boards are only 8.57” wide by 13.04” deep. Low profile (LPX) backplanes mount expansion slots on a bus riser that connects to the motherboard. ATX combines features from the AT and LPX designs. Related technologies include MiniATX and microATX. NLX, another form factor for backplanes, supports both current processors and technologies such as accelerated graphics port (AGP), universal serial bus (USB), and dual in-line memory module (DIMM). NLX cards are up to 9” wide and 13.6” deep. Other common form factors for backplanes include Size A (100 mm x 160 mm), Size B (233 x 160 mm), Size C (233 x 340 mm), and Size D cards (360 mm x 340 mm).

Important specifications for backplanes include the number of segments in the card and the number of expansion slots. Typically, active backplanes include a slot for plugging in the CPU. The bus type determines whether the backplane contains slots for ISA, PCI, cPCI, PXI, VME, VXI, or MXI slots. The form factor determines whether backplanes support AT, ATX, terminal block, or 3.3 V power connectors. Some backplanes include a connector for a keyboard. Others include on-board terminators that minimize reflections and interference on the bus.

• Elma Bustronic Announces New 16-Slot ATCA Backplane for ETSI Racks
  FREMONT, California, June 8, 2005 - Elma Bustronic Corporation, an industry leading designer and manufacturer of high performance backplanes has developed a new 16-slot AdvancedTCA (ATCA) backplane....
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• Elma Bustronic Develops Space Saving 3-Slot 3U CompactPCI Backplane
  FREMONT, California, July 19, 2005 - Elma Bustronic Corporation, an industry leading designer and manufacturer of high performance backplanes has developed space saving 3U CompactPCI backplane in a...
  (read more)
• Elma Bustronic's New 2-Slot AdvancedTCA Backplane Ideal for Prototyping
  FREMONT, California, May 3, 2005 - Elma Bustronic Corporation, an industry leading designer and manufacturer of high performance backplanes has developed a new 2-slot AdvancedTCA (ATCA) backplane. The...
  (read more)

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Part Numbers for Backplanes