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What is an Embedded System?

Definition
It is a system that has the computer hardware equipments guided by software instructions. An embedded system consists of microprocessor, primary memory, secondary memory, output unit and the network.
                                                            OR
An embedded system is a system that has embedded software and computer hardware, which makes it a system dedicated for an application(s) or specific part of an application or product or a part of a larger system.

Every embedded system consists of custom-built hardware built around a Central Processing Unit (CPU). This hardware also contains memory chips onto which the software is loaded. The software residing on the memory chip is also called the firmware. The embedded system architecture can be represented as a layered architecture. The operating system runs above the hardware, and the application software runs above the operating system. The same architecture is applicable to any computer including a desktop computer. However, there are significant differences. It is not compulsory to have an operating system in every embedded system. For small appliances such as remote control units, air-conditioners, toys etc, there is no need for an operating system and you can write only the software specific to that application. For applications involving complex processing, it is advisable to have an operating system. In such case, you need to integrate the application software with the operating system and then transfer the entire software on to the memory chip. Once the software is transferred to the memory chip, the software will continue to run for a long time and you don’t need to reload new software.
Now let us see the details of the various building blocks of the hardware of an embedded system.




Central Processing Unit (CPU)
The central Processing Unit (processor, in short) can be any of the following:
·         Microcontroller

A micro-controller is a low-cost processor. Its main attraction is that on the chip itself, there will be many other components such as memory, serial communication interface, analog-to-digital converter etc. So, for small applications, a micro-controller is the best choice as the number of external components required will be very less.

·         Microprocessor

On the other hand, microprocessors are more powerful, but you need to use many external components with them.

·         Digital Signal Processor (DSP)

DSP is used mainly for applications in which signal processing is involved such as audio and video processing.

Memory
The memory is categorized as Random Access Memory (RAM) and Read Only Memory (ROM). The contents of the RAM will be erased if power is switched off to the chip, whereas ROM retains the contents even if the power is switched off. So, the firmware is stored in the ROM. When power is switched on, the processor reads the ROM, the program is transferred to RAM and the program is executed.

Input Devices
Unlike the desktops, the input devices to an embedded system have very limited capability. There will be no keyboard or mouse, and hence interacting with the embedded system is no easy task. Many embedded systems will have a small keypad – you press one key to give a specific command. A keypad may be used to input only the digits. Many embedded systems used in process control do not have any input device for user interaction; they take inputs from sensors or transducers and produce electrical signals that are in turn fed to other systems.

Output Devices
The output devices of the embedded systems also have very limited capability. Some embedded systems will have a few Light Emitting Diodes (LEDs) to indicate the health status of the system modules, or for visual indication of alarms. A small LCD may also be used to display some important parameters.

Communication Interfaces
The embedded system may need to interact with other embedded systems or they may have to transmit data to a desktop. To facilitate this, the embedded systems are provided with one or a few communication interfaces such as RS232, RS422, RS485, Universal Serial Bus (USB), Ethernet etc.

Application specific circuitry
Sensors, transducers, special processing and control circuitry may be required for an embedded system, depending on its application. This circuitry interacts with the processor to carry out the necessary work.
The entire hardware has to be given power supply either through the 230 volts main supply or through a battery. The hardware has to be designed in such a way that the power consumption is minimized.

Resources Used:
1. Embedded Systems by Rajkamal  
2. Black Book

Compiled By: Chaudhary Amit V.
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