25-08-2017, 09:32 PM
GENERAL MICROPROCESSORS AND MICROCONTROLLERS
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INTRODUCTION
We are living in the age of information revolution, with computers of astonishing power available for our use. Computers find their way into every realm of activity. Some are developed to be as powerful as possible, without concern for price, for high-powered applications in industry and research. Others are designed for the home and office, less powerful but also less costly. Another category of computer is little recognised, partly because it is little seen. This is the type of computer that is designed into a product, in order to provide its control. The computer is hidden from view, such that the user often doesn’t know it’s even there. This sort of product is called an embedded system, and it is what this book is about. Those little computers we generally call microcontrollers.These days embedded systems are everywhere, appearing in the home, office, factory,car or hospital. The basic idea of an embedded system is a simple one. If we take any engineering product that needs control, and if a computer is incorporated within that product to undertake the control, then we have an embedded system.
MICROPROCESSORS
The first microprocessors appeared in the 1970s. These were amazing devices, which for the first time put a computer CPU onto a single IC. For the first time, significant processing power was available at rather low cost, in comparatively small space. At first, all other functions, like memory and input/output interfacing, were outside the microprocessor, and a working system still had to be made of a good number of ICs. Gradually, the microprocessor became more self-contained, with the possibility, for example, of including different memory types on the same chip as the CPU. At the same time, the CPU was becoming more powerful and faster, and moved rapidly from 8-bit to 16- and 32-bit devices. The development of the microprocessor led very directly to applications like the personal computer.
MICROCONTROLLERS
While people quickly recognised and exploited the computing power of the microprocessor, they also saw another use for them, and that was in control. Designers started putting microprocessors into all sorts of products that had nothing to do with computing, like the fridge or the car door that we have just seen.
Here the need was not necessarily for high computational power, or huge quantities of memory, or very high speed. A special category of microprocessor emerged that was intended for control activities, not for crunching big numbers. After a while this type of microprocessor gained an identity of its own, and became called a microcontroller. The microcontroller took over the role of the embedded computer in embedded systems. so what distinguishes a microcontroller from a microprocessor Like a microprocessor, a microcontroller needs to be able to compute, although not necessarily with big numbers. But it has other needs as well.
Primarily, it must have excellent input/output capability, for example so that it can interface directly with the ins and outs of the fridge or the car door. Because many embedded systems are both size and cost conscious, it must be small, self-contained and low cost. Nor will it sit in the nice controlled environment that a conventional computer might expect. No, the microcontroller may need to put up with the harsh conditions of the industrial or motor car environment, and be able to operate in extremes of temperature.Essentially, it contains a simple microprocessor