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EMBED THIS PC

PART 1: WHATýS IT ALL ABOUT?
by George Martin

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

SELECTING THE CPU

You begin by taking a look at the chips available. The obvious place to start looking is the individual manufacturers web sites (Intel, AMD, etc). You should also browse the EDN Annual Microprocessor Directory. I would also look at the 2000 Buyerýs Guide from Embedded Systems Programming. Sites like ChipCenter also provide a searchable database.

Youýll soon realize you have too much information. But, thatýs the good news. Thatýs why they invented large hard disks. Saving the data has to be better than waiting for all the catalogs and datasheets to arrive?

As youýll soon see, there are a number of ý486-class chips from a number of manufacturers. Youýll find the complete rangeýfrom true ý486s with floating-point math coprocessors to several hybrid versions with no math support, but much better on-chip peripheral support logic. None of these chips offer true second sources, and none are pin-compatible replacements. So, weýre going to break the number one rule for survival in this design businessýweýre going to design in sole-source parts.

The design decisions made in selecting the chip directly affect the overall performance, amount of peripheral circuitry required, packaging, and costs. Your CPU selection also dictates your design and development environment and the tools available and level of support youýll get. These areas have a significant impact on project costs.

As you might surmise, this selection process is only partially scientific. You canýt precisely fill out a spreadsheet with a complete analysis of different CPU choices. Count on reading articles such as this to look into other supporting information.

I believe the CPU that best fits into a typical embedded system is one that integrates many peripherals on-chip and sacrifices the floating-point math coprocessor. I do see a need for DRAM, EPROM, flash memory, and SRAM devices, as well as several external peripherals with their associated decodes and buses.

Also, if we select the classic Intel ý486DX chip, then we probably should purchase a board solution. Otherwise, it would take thousands of units to recover the design and startup costs.

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