About PC/104 Equipment

The Need For An Embedded PC Standard

Over the past decade the enormous popularity of the PC architecture has driven it beyond its originally intended "personal" desktop realm. Dedicated and embedded applications for PC's are beginning to show up everywhere! PC's are used as controllers within vending machines, laboratory instruments, communications devices, and medical equipment. A need arose for a more compact implementation of the PC BUS that could accommodate the reduced space and power constraints of embedded applications. Yet these goals have to be achieved without sacrificing full hardware and software compatibility with the PC's hardware and software development tools and system design knowledge to be fully leveraged.

A Proposed Extension To IEEE-P996

PC/104 was developed to meet this need. It offers full architecture, hardware and software compatibility with the PC BUS, but in ultra-compact (3.6 x 3.8 in), stackable modules ideally suited to the unique requirement of embedded control applications. Although PC/104 modules have been manufactured since 1987, a formal specification was not published until 1992. Since then, interest in PC/104 has skyrocketed, with numerous PC/104 modules introduced by more than 125 manufactures of PC/104-compatible products. Like the original PC BUS its self, PC/104 has thus the expression of the de facto standard, rather than the invention and design of a committee. In 1992, the IEEE began a project to standardise a reduced form factor implementation of the IEEE P966 (draft) specification for the PC and PC/AT buses, for embedded applications. The PC/104 Specification has been adopted as the "base document" for this new IEEE standard, called P996.l standard for Compact Embedded PC Modules.

The Key difference between the PC/104 and PC BUS (IEEE) are:

• Compact Form Factor - Size reduced by 3.6 by 3.8 inches.
• Unique Self Stacking Bus - Eliminates the cost of buying backplanes and card cages.
• Pin And Socket Connectors - Rugged and reliable 64- and 40- contact male/female headers replace the standard edgecard connectors.
• Relaxed Bus Drive (4mA) - Lowers power consumption (to 1-2 watts per module) and minimised component count.

History

PC/104 is derived from the "Mini Module" form factor, originally developed in 1987 as a plug in expansion module standard for the Ampro "Little Board" family of single board computer. In 1990 Ampro introduced the first CPU module in a Mini Module form-factor, and along with it, the unique self stacking BUS concept.

Two Ways To Use PC/104 Module

Although configurations and application possibilities with PC/104 are limitless. There are two basic ways they tend to be used in embedded designs:

• Stand alone module stacks.
  PC/104 modules are self stacking. In this approach the modules are used like ultra compact BUS boards, but without the need for back planes or card cages. Stacked modules are placed .6 inches apart when installed. The three module stack measures just 3.6 by 3.8 by 2 inches.

• Component like application.
  In this type of application the modules function as highly integrated components, plugged into custom carrier boards which contain application specific interfaces and logic. The modules' self stacking ability can be useful for installing multiple modules in one location. This facilitates future upgrades or options. For More information see the PC/104 web site at www.controlled.com.

PC/104 Specification

The PC/104 specification is available for download in Adobe Acrobat format. To download, click here (version 2.5)