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U. Glaeser

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that is connected to Port A, if the temperature is above 73°<br />

F, it turns off the heat (by writing 0 to Port B).<br />

If the temperature is below 68°<br />

F, it turns on the heat by writing 1 to Port B.<br />

Embedded Microcomputer<br />

During the development phases of a project, we often would like the flexibility of accessing components<br />

inside the single-chip computer. In addition, during development, we are often unsure of the memory<br />

size and I/O capabilities that will be required to complete the design. Both of these factors point to the<br />

need for a single-board computer. This board has all of the features of the single-chip computer but laid<br />

out in an accessible and expandable manner. For some microcomputer systems, the final product is delivered<br />

using a single-board computer. For example, if the production volume is small and the project does not<br />

have severe space constraints, then a single-board solution may be cost-effective. Another example of final<br />

product delivered with a single-board occurs when the computer requirements (memory size, number<br />

of ports, etc.) exceed the capabilities of any single-chip computer.<br />

Choosing a Microcomputer<br />

The computer engineer is often faced with the task of selecting a microcomputer for the project. In 1997<br />

Motorola had 17.4% of the 4/8/16+ bit microcontroller market, Hitachi had 15.6%, and NEC had 13.2%.<br />

Table 23.2 breaks the 8-bit market share down by architecture, showing the 8051 architecture to be most<br />

popular. As of 1997, Motorola has shipped over 2 billion 68HC05 8-bit microcontrollers. This cumulative<br />

number on a unit level is more than all microprocessors from all other chip vendors. Table 23.3 lists<br />

major manufacturers and their web sites<br />

Often, only those devices for which the engineers have hardware and software experience are considered.<br />

Fortunately, this blind approach often still yields an effective and efficient product, because many<br />

of the computers overlap in their cost and performance. In other words, if a microcomputer that you<br />

are familiar with can implement the desired functions for the project, then it is often efficient to bypass that<br />

perfect piece of hardware in favor of a faster development time. On the other hand, sometimes one wishes<br />

to evaluate all potential candidates. Sometimes, it may be cost-effective to hire or train the engineering<br />

© 2002 by CRC Press LLC<br />

TABLE 23.2<br />

1997 Market Share in Dollars of 8-bit Microcontrollers [1]<br />

µ C Company Revenue (millions)<br />

8051 Intel, Philips, Siemens, Dallas Semiconductor 1027<br />

HC05 Motorola 864<br />

HC11 Motorola 643<br />

H8 Hitachi 505<br />

78K NEC 497<br />

TABLE 23.3<br />

Web Sites of Companies That Make Microcontrollers<br />

Company Products Web Site<br />

Motorola HC05 HC08 HC11 HC12<br />

HC16 683xx 68K<br />

MCORE Coldfire<br />

PowerPC<br />

http://www.motorola.com/<br />

Hitachi H8 http://www.hitachi.com/<br />

NEC 78K http://www.nec.com/<br />

Intel 8051 80251 8096 80296 http://www.intel.com/<br />

Mitsubishi 740 7600 7700 M16C http://www.mitsubishichips.com/index.htm<br />

Philips 8051 http://www.philips.com/home.html<br />

Siemens C500 C166 Tricore http://www.siemens.de/en/<br />

Microchip PIC12 PIC12 PIC16 PIC17 http://www.microchip.com/

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