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PART 1: WHATıS IT ALL ABOUT?
by George Martin

Start ı Narrowing Specs ı Selecting the CPU ı Packaging ı The Software ı Memory ı Your Job ı Sources and PDF

NARROWING SPECS

Letıs start with what an embedded ıı486 system is. Why canıt I just buy a regular ı486? Shouldnıt I be looking at a Pentium?

Let me define some of the goals of this project. Letıs attempt to design a ı486 machine (on paper) that can run a multitude of software but still process data at a high speed. The application Iıll use as the typical application or reference point is the controller for laser light shows. The light beams are guided across the sky by mirrors and those mirrors are driven as fast as possible, because you canıt go faster than the speed of light anyway. The faster the CPU, the better the light show.

I could also have used a machine-tool path as the typical application. Both are good designs to focus on because they have command inputs, sensor flags, and DAC outputs. Itıs all fairly straightforward.

In narrowing the article prototype to this example, I hope not to exclude all the other possible designs that an embedded ı486 system could accomplish. What Iıll cover also accommodates a hard or floppy disk and runs a commercial OS.

Another area of design consideration is size and power. Fortunately for us, integrated circuits have been following Mooreıs Law. Every 18 months, they shrink in size by a factor of two. I donıt think a 100-W system is in keeping with our embedded world, so letıs design a system where the CPU and memory use less than 3 W.

The size should be about that of a cigar box or, to make things more politically correct, a lunch box. Obviously, size is an area where your specific application needs more voice in the matter. Donıt forget, you can use double-sided or multilayer boards. Of course, double-sided boards are much larger and less difficult to build than a multilayer design. Soon, however, the higher density of surface-mount packages will make fine lines and multilayer designs about the same price as double-sided boards.

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