Embedded Systems and Microcontrollers

Embedded Systems

An embedded system is a computer system which is mainly used to get  a specific set of functions done depending on a set of constraints. More often embedded systems are “embedded” into a larger system to get a specific task done, but often not too complex as the whole system which it is embedded in.

Many day to day devices in modern world are embedded with these kinds of systems. For an example digital watches, mobile phones, factory automation systems, modern LED and LCD televisions and etc. Most of these devices are portable devices as one can expect them to be.

History

                The first modern embedded system is considered as the Apollo Guidance Computer, developed by Charles Stark Draper at the MIT Instrumentation Laboratory. This system controlled the path of the flight and some landing issues by taking various data input from the ground control station as well as from the built in sensors. Also few years later the Minuteman missile was built around an embedded system which controlled the path of flight of the missile. More over this is considered to be the first widely produces embedded system.

Introduction

In embedded systems, mainly two types of controllers are used. They are Microcontrollers and DSPs (Digital Signal Processors). In this article the main focus will be on microcontrollers. We will be discussing some available microcontrollers today and some of their functionalities as well.

A microcontroller can be considered a self-contained system with a processor, memory and peripherals and can be used as an embedded system. A microcontroller (sometimes abbreviated µC, uC or MCU) is a small computer on a single integrated circuit containing a processor core, memory, and typically small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications. Actually microcontrollers can be considered as a small scale version of microprocessors.

These microcontrollers have Rams ranging from kilo bytes to several hundred mega bytes. Some microcontrollers may use four-bit words and operate at clock rate frequencies as low as 4 kHz, for low power consumption (mill watts or microwatts) while some other microcontrollers have clock rates nearly hundreds of mega hertz.

A Block diagram showing the main components of PIC (Peripheral interface Controller) Microcontrollers

Main Components of Microcontrollers

Read Only Memory (ROM)

Read Only Memory (ROM) is a type of memory used to permanently save the program being executed. The size of the program that can be written depends on the size of this memory. ROM can be built in the microcontroller or added as an external chip, which depends on the type of the microcontroller.

Random Access Memory (RAM)

Random Access Memory (RAM) is a type of memory used for temporary storing data and intermediate results created and used during the operation of the microcontrollers.

Electrically Erasable Programmable ROM (EEPROM)

The EEPROM is a special type of memory not contained in all microcontrollers. Its contents may be changed during program execution (similar to RAM), but remains permanently saved even after the loss of power (similar to ROM

Special Function Registers (SFR)

Special function registers are part of RAM memory. Their purpose is predefined by the manufacturer and therefore cannot be changed. Since their bits are physically connected to particular circuits within the microcontroller, such as A/D converter, serial communication module etc.

Program Counter

Program Counter is an engine running the program and points to the memory address containing the next instruction to execute. After each instruction execution, the value of the counter is incremented by 1.

Central Processor Unit (CPU)

                As its name suggests, this is a unit which monitors and controls all processes within the microcontroller and the user cannot affect its work. It consists of several smaller subunits, of which the most important are:

·       Instruction decoder.

·       Arithmetical Logical Unit (ALU)

·       Accumulator is an SFR closely related to the operation of ALU.

Pros and Cons

Among the main advantages of microcontrollers, the ability to write its’ inner non volatile (Electrically Erasable Programmable ROM (EEPROM)) as many as 10000 times is a main advantage. This enables the developers to imply trial and error method without too many complications and also this allows having cheap solutions for multiple systems since one does not need to replace the microcontroller. Also the power consumption for microcontrollers are very much low and this allows to run the system for more time duration without any difficulty. Further, in today’s market microcontrollers are available from few hundred rupees on wards and this make developer to develop very cheap solutions even for large scale problems. More over special function registers are present in all most all the microcontrollers available today and this make the solution reviling more easily.

Although there are many advantages, one cannot really say there are disadvantages in embedded systems except the limitation of the processing power. After all microcontrollers are built to implement solutions that can be gained through low processing power. Also a light problem with these microcontrollers is Brown out. Brown out is a potentially dangerous state which occurs at the moment the microcontroller is being turned off or when power supply voltage drops to the lowest level due to electric noise.

By- Tharidu Rathnayake