Embedded Systems Design - March 2008 - (Page 41)

0308esd.p41to46 2/14/08 12:17 PM Page 41 20 years ago The following article ﬁrst appeared in the At the Bench column in the March 1989 issue of Embedded Systems Programming magazine. Programming L your own microcontroller BY ERNEST L. MEYER ast month* we discussed the differences between general-purpose programming languages and hardware description languages (HDLs). This month we’ll look at how HDLs can be used to design embedded systems directly. Rather than using a general-purpose language to program an embedded processor, you can use an HDL to configure a programmable logic device (PLD). A number of special sets of HDLs are specifically designed to configure PLDs. Originally, PLDs contained fuses and fusemaps generated from the HDL descriptions of the desired functionality. Although fused devices are still used, modern PLDs can also use programming techniques; higher densities, as well as higher speeds, can be obtained. Indeed, the most sophisticated PLDs available contain over 600 register bits and operate at clock speeds in excess of 70 MHz. Since the register bits can easily be configured in any width and linked with any logical structure, these larger PLDs are a viable and faster alternative to any microcontroller architecture. These PLDs do tend to cost hundreds of dollars, however. Although they can be priced competitively if they can directly replace an ultrahigh-performance 32-bit microcontroller or application-specific processor, they’re beyond the budget of most embedded applications. Smaller PLDs, which cost only a few dollars, offer a viable alternative to small microcontrollers in small- and medium-run quantities. Because no separate PROM is required, one chip can be sufficient for applications that would require at least two chips if a low-cost microcontroller were used. Though microcontrollers can be economically mask programmed in sufficient volume to offset the price difference, PLDs offer architectural advantages that can make them *Editor’s note: Remember, this article was written 20 years ago. When this article was written 20 years ago, the FPGA was only ﬁve years old and not widely used yet. Here’s an early how-to article on PLD design that stands the test of time. www.embedded.com | embedded systems design | MARCH 2008 41 http://www.embedded.com

Table of Contents Feed for the Digital Edition of Embedded Systems Design - March 2008

Embedded Systems Design - March 2008 Contents #Include Programming Pointers Designing DSP-based Motor Control Using Fuzzy Logic Hardware/Software Verification Enters the Atomic Age Efficient CRC Calculation with Minimal Memory Footprint Programming Your Own Microcontroller Advertising Index Break Points Marketplace

Embedded Systems Design - March 2008

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