PC/104 Standard Overview
The Need for an Embedded-PC Standard
Over the past decade, the PC architecture has become an accepted platform for far more than desktop applications. Dedicated and embedded applications for PCs are beginning to be found everywhere! PCs are used as controllers within vending machines, laboratory instruments, communications devices and medical equipment, to name a few examples.
By standardizing hardware and software around the broadly supported PC architecture, embedded system designers can substantially reduce development costs, risks and time. This means faster time-to-market and hitting critical market windows with timely product introductions. Another important advantage of using the PC architecture is that its widely available hardware and software are significantly more economical than traditional bus architects such as STD, VME and Multibus. This means lower product costs.
For these reasons, companies that embed microcomputers as controllers within their products seek ways to reap the benefits of using the PC architecture. However, the standard PC bus form- factor (12.4" x 4.8") and its associated card cages and backplanes are too bulky (and expensive) for most embedded control applications.
The only practical way to embed the PC architecture in space and power-sensitive applications has been to design a PC - chip-by- chip - directly into the product. This runs counter to the growing trend away from "reinventing the wheel." Wherever possible, top management now encourage outsourcing of components and technologies to reduce development costs and accelerate product design cycles.
A need therefore arose for a more compact implementation of the PC bus, satisfying the reduced space and power constraints of embedded control application. Yet these goals had to be realized without sacrificing full hardware and software compatibility with the popular PC bus standard. This would allow the PC's hardware, software, development tools and system design knowledge to be fully leveraged.
PC/104 was developed in response to this need. It offers full architecture, hardware and software compatibility with the PC bus, but in ultra-compact (3.6" x 3.8") stackable modules. PC/104 is therefore ideally suited to the unique requirements 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 the more than 125 manufacturers of PC/104-compatible products. Like the original PC bus itself, PC/104 is thus the expression of a defacto standard rather than the invention and design of a committee.
In 1992, the IEEE began a project to standardize a reduced form- factor implementation of the IEEE P996 (draft) specification for th PC and PC/AT buses for embedded applications. The PC/104 Specification has been adopted as the "base document" for this n IEEE draft standard, called the P996 I Standardfor Compact Embedded PC Modules.
The key differences between PC/104 and the regular PC bus (IEEE P996) are:
Basic mechanical Dimensions (8 bit Version)
Although configuration and application possibilities with PC/104 modules are practically limitless, there are two basic ways they tend to be used in embedded system designs: