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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

Microprocessor

A microprocessor popularly known as "computer on a chip" in its early days, is a central processing unit commonly used (CPU) manufactured in a single integrated circuit (IC) and is a complete digital computer (microcontroller later considered more precise form of the complete computer). It is a small but very powerful electronic brain that operates at a blistering speed and is often used to carry out the instructions of a computer program to perform arithmetic and logic operations, store data, control the system, input / output etc. according to the instructions. The key term in the definition of a microprocessor is "general purpose". This means that, with the help of a microprocessor, one can build a simple system or a large and complex machine around it with some additional components depending on the application. The main task of a microprocessor is to accept data as input from input devices, then process this data in accordance with the instructions and provide the output of these instructions as output through output devices. The microprocessor is an example of a sequential logic device since it has internal memory and uses it to store instructions.

The first commercial Microprocessor was released by Intel in the year 1971 November named as 4004 (four-thousand-four). It is a 4-bit microprocessor.

There are five important components in a microprocessor. They are arithmetic and logical units (ALU), control unit, registers, instructions decoder and data bus, but the first three are considered significant components. The block diagram of a microprocessor with these basic components is shown below.

[Image: BLOCK-DIA-OF-MP.jpg]

The internal structure of a microprocessor is shown below.

[Image: INTERNAL-STRUCTURE-OF-MP.jpg]

Previous microprocessors used the Von Neumann architecture where data and instructions (programs) are stored in the same memory. Although this architecture is simple, there are many backs. One of the main drawbacks is that the instruction and data can not be accessed while sharing a single data bus. This often degrades the overall performance of the device. Subsequently, the Harvard architecture is introduced, which uses separate program and data memories with separate buses, so that data and instructions can be accessed at the same time. Subsequently the Harvard modified architecture was developed, in which the program memory is accessed as if it were a data memory.

[Image: VON-NEUMANN-VS-HARVARD.png]

There are three basic features used to differentiate microprocessors. They are set of instructions, bandwidth and clock speed. The set of instructions is related to the programming of the microprocessor consisting mainly of instructions that a microprocessor can execute. Bandwidth indicates the maximum number of bits processed in a single instruction. The clock speed does not. of instructions that a processor can execute per second. Normally the clock speed is in MHz (Mega Hertz) or GHz (Giga Hertz). In general, the characteristics of bandwidth and clock speed are looked at together. The higher the values of both features, the more powerful the processor.

The instruction set or instruction set architecture (ISA) also plays an important role in the design and operation of a processor. The microprocessors are classified as CISC (Complex Instruction Set Computer) or RISC (Small Instruction Set Computer).

The CISC architecture consists of a complete set of instructions that are complex, larger, have more computational power, and so on. A single CISC instruction can be used to perform various low-level operations, multi-step operations, and multiple addressing modes. The execution time of these instructions is long. The Intel X86 is an example of CISC architecture.
The RISC architecture was developed by realizing that instead of using a complete set of instructions, only frequently used instructions are sufficient. In this architecture, the instructions are small and highly optimized. RISC processors are used where the execution time of the instruction must be lower and the development cost is lower. ARM devices are based on the ARM architecture which is a subset of RISC.

Microcontroller

The main reason for the development of the microcontroller is to overcome the only drawback of the microprocessor. Although microprocessors are powerful devices, they require external chips such as RAM, ROM, input / output ports, and other components to design a complete work system. This made it economically difficult to develop computerized consumer devices on a large scale since the cost of the system is very high. Microcontrollers are devices that actually fit into the "Computer on a Chip" profile, as it consists of a main processing unit or processor along with some other components that are required to make it a complete computer. The components that are present in a typical IC of a microcontroller are CPU, memory, I / O ports and timers. The first microcontroller was developed in 1971 by Texas Instruments and is called TMS 1000. It was made available for commercial use in 1974. The block diagram of a microcontroller is shown below.

[Image: BLOCK-DIA-OF-MC.png]

Microcontrollers are basically used in embedded systems. The computerized or digital control of the devices becomes plausible with the development of microcontrollers. The development process of the microcontroller is similar to that of a microprocessor.

Microcontrollers can be classified according to bus width, memory structure and instruction set. The width of the bus indicates the size of the data bus. Microcontrollers can be classified as 8-bit, 16-bit or 32-bit based on the bus width. Higher bus widths often result in better performance. Microcontrollers can be divided into two types based on their memory structures: integrated memory and external memory. In the case of built-in memory microcontrollers, the required data and program memory are embedded in the IC. While the external memory microcontrollers do not have program memory embedded in them and require an external chip for it. Today, all microcontrollers are built-in memory microcontrollers. The classification based on the set of instructions is similar to that of a microprocessor. They can be CISC or RISC. Most microcontrollers follow the CISC architecture with more than 80 instructions. Microcontrollers can also be divided according to their computer architecture in von Neumann and Harvard.

The following table exemplifies some of the differences between microprocessors and microcontrollers.

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