Programming Embedded Systems, 2nd Edition

Embedded Design Examples

To demonstrate the variation in design requirements from one embedded system to the next, as well as the possible effects of these requirements on the hardware, we will now take some time to describe three embedded systems in some detail. Our goal is to put you in the system designer’s shoes for a few moments before narrowing our discussion to embedded software development.

Digital Watch

At the current peak of the evolutionary path that began with sundials, water clocks, and hourglasses is the digital watch. Among its many features are the presentation of the date and time (usually to the nearest second), the measurement of the length of an event to the nearest hundredth of a second, and the generation of an annoying little sound at the beginning of each hour. As it turns out, these are very simple tasks that do not require very much processing power or memory. In fact, the only reason to employ a processor at all is to support a range of models and features from a single hardware design.

The typical digital watch contains a simple, inexpensive 4-bit processor. Because processors with such small registers cannot address very much memory, this type of processor usually contains its own on-chip ROM. And, if there are sufficient registers available, this application may not require any RAM at all. In fact, all of the electronics— processor, memory, counters, and real-time clocks—are likely to be stored in a single chip. The only other hardware elements of the ...