About PC/104+ & PCI-104 Equipment
The PC/104-Plus specification establishes a standard for the use of a high speed PCI bus in embedded applications. Incorporating the PCI bus within the industry proven PC/104 form-factor brings many advantages to its users, including fast data transfer over a PCI bus, low cost due to PC/104's unique self-stacking bus, and high reliability due to PC/104's inherent ruggedness.
A Proposed Extension To IEEE-P996
A PCI-enhanced version of PC/104 was developed and offered to the PC/104 Consortium in September 1996. The Consortium formed a working group to review and finalize the specification, and PC/104-Plus was subsequently approved by the Consortium's voting members in February 1997.
The main objective in defining an addition of PCI to PC/104 was to preserve the attributes that have made PC/104 so successful in embedded applications, namely:
In addition, it was important that the new embedded form of PCI also be . . .
This added requirement enables newly designed PC/104-Plus modules
to be used in conjunction with the wide variety of preexisting PC/104
Two Ways To Use PC/104 Module
The diagram below shows the basic mechanical dimensions of a PC/104-Plus module. The module's form-factor matches that of PC/104, so PC/104-Plus can be said to be "PC/104 form-factor compliant". The new self-stacking 120-pin high-density (2 mm) PCI bus connector fits between the standard PC/104 mounting holes along the edge opposite the regular PC/104 (ISA) bus, so it consumes minimal space (approximately 10%).
Here is a brief summary of the basic specs of PC/104-Plus modules:
The diagram below illustrates a typical PC/104-Plus stack. 8- and 16-bit PC/104 (ISA) modules can be stacked along with 32-bit PC/104-Plus (PCI) modules, provided that similar type modules are adjacent to each other. This results in maximum system expansion and configuration flexibility.
PC/104-Plus, like PC/104, is essentially a repackaged version of PCI that is optimised for the unique requirements of embedded systems - where space is scarce and ruggedness is paramount. Although PC/104-Plus modules provide connectors for both buses, the "120-pin PCI bus" and the "104-pin ISA bus," only the PCI bus usually connects to circuitry on such a module. The ISA bus connectors are only there to pass the ISA bus on for possible use by the next module in a stack.
Current status of the PC/104-Plus standard
PC/104-Plus shows every indication of following in the footsteps of its predecessor. Numerous companies have announced support or begun development programs based on PC/104-Plus. Products being developed include high performance single-board computers, full-motion video interfaces, high speed LANs, communications interfaces (100BaseT, USB, IEEE-1394, etc.), high performance data acquisition and control interfaces, and PCI bus adapters and bridges. A copy of the PC/104-Plus Specification is available to download below.
PC/104+ & PCI-104 Specification
The PC/104+ specification is available for download in Adobe Acrobat
format. To download, click here (version 2.2)
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