Jul 21, 2014

Fundamentals of Embedded Systems

Microcontroller Overview:

What is a Microcontroller?

A microcontroller is a single chip, self-contained computer which incorporates all the basic components of a personal computer on a much smaller scale. Microcontrollers are often referred to as single chip devices or single chip computers. The main consequence of the microcontroller’s small size is that its resources are far more limited than those of a desktop personal computer. In functional terms, a microcontroller is a programmable single chip which controls a process or system. Microcontrollers are typically used as embedded controllers where they control part of a larger system such as an appliance, automobile, scientific instrument or a computer peripheral. Microcontrollers are designed to be low cost solutions; therefore using them can drastically reduces part and design costs for a project.Physically, a microcontroller is an integrated circuit with pins along each side. The pins presented by a microcontroller are used for power, ground, oscillator, I/O ports, interrupt request signals, reset and control. In contrast, the pins exposed by a microprocessor are most often memory bus signals (rather than I/O ports).
A microcontroller is not the same as a microprocessor. A microprocessor is a single chip CPU used within other computer systems. A microcontroller is itself a single chip computer system.

Personal computers are used as development platforms for microcontroller projects. Development computers, usually personal or workstation computers, use a microprocessor as their principle computing engine. Microprocessors depend upon a variety of subsidiary chips and devices to provide the resources
not available on the microprocessor. Additional chips required with aprocessing. A development platform is required to run embedded system development software such as assemblers, compilers, editors and simulators which require the processing power and memory capabilities of a desktop personal computer
or workstation. The target platform is the platform on which the finished program will be run.
For example, consider a developer who is creating a program for a Motorola 68HC705C8 microcontroller. The developer writes, edits, and tests the program on a Pentium 133 personal computer: the development platform. The developer will use software which runs on a Pentium 133 but whose target device is the 68HC705C8. When the program is ready it is programmed in the target platform, the 68HC705C8.
A microcontroller has seven main components:
1. Central processing unit (CPU)
2. ROM
3. RAM
4. Input and Output
5. Timer
6. Interrupt circuitry
7. Buses

Figure 1: The microcontroller

The Microcontroller in a System:

Microcontrollers do not function in isolation. As their name suggests they are designed to control other devices. The microcontroller can accept inputs from some devices and provide outputs to other devices within any given system. For example, a microcontroller may accept input from a switch and may send
output to an LED. If the switch is pressed the microcontroller can be instructed to illuminate the LED.
The microcontroller is often part of a larger system. For example, the switch and LED may be part of a compact disc player in a car stereo system. When a microcontroller is part of a larger system it is often referred to as an embedded controller because it is embedded within the larger system.


There are two basic types of architecture: Harvard and Von Neumann. Microcontrollers most often use a Harvard or a modified Harvard-based architecture.

von Neumann architecture and Harvard architecture

The von Neumann architecture is a computer design model that uses a processing unit and a single separate storage structure to hold both instructions and data. It is named aftermathematician and early computer scientist John von Neumann. Such a computer implements a universal Turing machine, and the common "referential model" of specifyingsequential architectures, in contrast with parallel architectures. The term "stored-program computer" is generally used to mean a computer of this design, although as modern computers are usually of this type, the term has fallen into disuse.http://en.wikipedia.org/wiki/Von_Neumann_architecture
Harvard architecture is a computer architecture with physically separate storage and signal pathways for instructions and data. The term originated from the Harvard Mark I relay-based computer, which stored instructions on punched tape (24 bits wide) and data in electro-mechanical counters (23 digits wide). These early machines had limited data storage, entirely contained within the data processing unit, and provided no access to the instruction storage as data, making loading and modifying programs an entirely offline process.

No comments:

Post a Comment

Than 'Q'