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Data Bus

Data bus architectures use 16, 32 or 64 bit data paths. Wider bus structures allow significant increases in data transfer rates.

Mil Std 1553 The current 1553B data bus is widely used in military applications. It is a 16-bit architecture with a nominal throughput of 1 Mb/s. Many existing military avionics systems are compatible with the 1553, but most new commercial systems are not. New commercial and some military applications use the VME or PCI bus architectures, or proprietary solutions. Mil-Std 1553B was adopted in 1978 and served well, but bandwidth is becoming a limiting factor.

Optic Fiber Mil-Std-1773 defines a fiber optic bus. This system is widely used for on-board command and telemetry transfer between military spacecraft components, subsystems and instruments, and within complex components themselves. 1773 systems achieve a 1 Mb/s data rate at 32 bits, but the AS 1773 implementation, now in development, has a dual rate of 1 Mb/s or 20 Mb/s. Fiber optic systems are uniquely resistant to radiation and other electro-magnetic environment effects.

VersaModule Eurocard (VME) Bus VME, developed by combining the commercial Motorola Versa bus and Signetics', Mostek's and Thompson CSF's Eurocard format, is now defined by the IEEE P1014-1987 standard. It is widely used in industrial, commercial and military applications with over 300 manufacturers of VME bus products worldwide. VME is based on 680xxx family of processors. VME is a 32-bit architecture with a 40 Mb/s throughput.

Peripheral Component Interconnect (PCI) Bus PCI is in widespread use in the computer industry. Although PCI was developed by Intel, it is not tied to any specific processor. It appears that PCI may eventually replace the older ISA bus and is competing with VME for industrial use. PCI can be 32 or 64-bits wide. It has peak transfer rates of 132 Mb/s, with a sustained transfer rates around 25 Mb/s. The PCI standard is maintained by the PCI Manufacturers Group with the electrical interface defined by IEEE P1386.1.

Futurebus+ Futurebus+ was designed to offer great potential throughput up to 500-600 Mb/s, as well as a large (300mm x 300mm) board size for installation of peripherals. It is supported by a fully developed IEEE standard (ANSI/IEEE 896). Although it is an open interface, only 3 or 4 manufacturers actually produce to it. One drawback to Futurebus+ is the larger board size, requiring more volume than the other types of interfaces that have smaller form factors. Typical throughput is 100-125 Mb/s at 32 bits.

VersaModule Eurocard (VME64) Bus With VME lagging the improved performance of PCI and Compact PCI, the VME group extended throughput with the VME64 configuration. VME64 expands the architecture to a 64 bit data path. VME64 is also backward compatible with VME. Performance is 80 Mb/s throughput on a 64 bit pathway.

ARINC 429 Aeronautical Radio Inc's Airlines Electronic Engineering Committee (a group affiliated with and supported by major international airline carriers and manufacturers) manages ARINC Standard 429 - "Mark 33 Digital Information Transfer System" for a commercial aircraft data bus. It is widely implemented in the commercial aircraft avionics industry. Performance is 100Kb/s or 12.5Kb/s at either 25 or 32 bits.

Systems Interface Bus (SIB) SIB is a proprietary bus structure, developed for earlier modifications in the B-52 and limited high performance applications. It is used in other parts of the current aircraft architecture. SIB is also employed for signal processing applications in the commercial market. LeCroy, the manufacturer, is migrating its new products to other interfaces. Performance is 5 Mb/s at 16 bits.

Industry Standard Architecture (ISA) bus This bus architecture was developed by IBM for the PC/XT and PC/AT and adopted for industrial applications. The ISA architecture is a defacto standard, still in wide use where high performance is not necessary. ISA is being replaced by the PCI bus for high performance applications in desktop computers. Today's desktop computers include both ISA and PCI buses, allowing backward compatibility for older components with a migration path for high performance solutions. Performance is 3 Mb/s at 16 bits.

Description Controlling Standard and Date Market Acceptance Performance Notes
1553 Data Bus Mil Std 1553B (1978)  Most US military aircraft systems now 1553 based. 1 Mb/s throughput at 16 bits  
Optic Fiber Mil Std 1773 (1989) Widely used in space craft systems 1 Mb/s throughput, 32 bits (Dual rate AS 1773 in development to provide 1 Mb/s or 20 Mb/s) Used for on-board command and telemetry transfer between spacecraft components and subsystems
VME bus IEEE P1014-1987 (developed from Motorola VersaBus) (1981) Over 200 manufacturers, wide application in industrial and commercial computing, also significant military application 40 Mb/s sustained throughput at 32 bits. Extension of the 68xxx microprocessor technology, 32 bit architecture. Current trend is use of mezzanine buses with VME backplane to increase capability.
PCI bus (Peripheral Component Interconnect) PCI-SIG 2.1 Local Bus Specification (1987) Widely used in commercial PC market 132 Mb/s peak throughput at 32 bits, (25 Mb/s sustained), 264 Mb/s peak throughput at 64 bits Originally based on x86/DOS processor technology
Futurebus+ IEEE 896.5a (1994) Proposed for military applications 100 Mb/s at 32 bits Advertised potential throughput 500 Mb/s; board size 300mmx300mm - twice the size of VME. Few manufacturers. High cost.
VME64 ANSI/VITA 1-1994 (1995) Developed from VME standard, expected to be produced by many of current VME manufacturers 80 Mb/s sustained at 64 bits (proposed upgrade to 160 Mb/s stalled by development problems) In production. Growth potential with VME320, with 320 Mb/s throughput is in development
Mark 33 Digital Information Transfer System ARINC 429 (1977) Commercial aircraft data bus 100Kb/s or 12.5Kb/s at 25 or 32 bits Wide use in the commercial aircraft avionics industry.  
SIB (Systems Interface Bus) LeCroy P1123 (1990) Proprietary bus, some military applications 5 Mb/s throughput at 32 bits  
ISA IEEE P-1882.1 (1996) (From IBM P-ISA, 1982) De facto industry standard for commercial PC until 3 Mb/s throughput at 16 bits Widely used in commercial PC applications

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