What is a Microcontroller?
Microcontrollers are semiconductors that are inside a surprising number of products. Most of your kitchen appliances have a microcontroller, which is obvious when they have a light emitting diode (LED) or liquid crystal display (LCD) screen and a keypad (like the one on your microwave oven). However, even newer appliances without screens, like toasters and blenders, often have microcontrollers inside. All modern automobiles contain at least one microcontroller, and can have up to 50 or more. The average new car contains 20 – 25 microcontrollers that are used in areas like engine control, anti-lock brakes, cruise control and air bags. Any device or appliance that has a remote control almost certainly contains a microcontroller. In fact, most consumer electronics, such as digital cameras, cell phones, camcorders, answering machines, laser printers, telephones with special features, pagers, high-tech refrigerators, dishwashers, and washers and dryers, have microcontrollers.
A microcontroller is a whole computer on one chip (often called a system-on-a-chip), while your desktop computer has many different pieces that work together inside that beige box. All computers have commonalties, whether a desktop personal computer (PC) or a large mainframe system. They all have a central processing unit (CPU) to execute a program, some random access memory (RAM) to store “variables,” erasable programmable read-only memory (EPROM), input/output (I/O), timers, and an interrupt controller. Desktop PCs are “general purpose computers” that can run thousands of programs. Microcontrollers are “special purpose computers” that are programmed to do a small number of things well, and are beneficial when all or most of the internal components are needed on one chip. Other common characteristics that define microcontrollers include:
• Microcontrollers are “embedded” (or hidden) inside some other device to control the features or actions of that product. Therefore, a microcontroller is synonymous with “embedded controller.” • Microcontrollers are dedicated to one task and run one specific program. The program is stored in on-chip program memory and generally does not change. Newer microcontrollers have Flash memory, which can be reprogrammed up to a million times. • Microcontrollers are often low-power devices. A desktop computer is almost always plugged into a wall socket and might consume 50 watts of electricity, while a battery- operated microcontroller may consume only one thousandth as much power (50 milliwatts). • A microcontroller has a dedicated input device and often, but not always, has a small LED or LCD screen for output. A microcontroller also takes input from the device it is controlling, and runs the device by sending signals to different components in the device. For example, the microcontroller inside a microwave oven takes input from a keypad, displays output on an LCD display, and controls a relay that turns the microwave generator on and off. Some microcontrollers are able to connect to the Internet or other networks, which is useful for applications like vending machines, enabling stock to be checked from a remote location. • A microcontroller is often small and low cost. These components are chosen to minimize size and to be the least expensive possible.
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• A microcontroller must frequently be durable, especially in automotive, commercial and industrial applications. For example, the microcontroller controlling a car’s engine works in extreme temperatures that a normal desktop computer generally cannot handle. A car’s microcontroller in Alaska has to work in -30°F (-34°C) weather, while the same microcontroller in Nevada might operate at 120°F (49°C). When you add the heat naturally generated by the engine, the temperature can go to more than 250°F (100 – 125°C) in the engine compartment. On the other hand, a microcontroller embedded inside a VCR doesn’t need to be as durable. • The actual processor (or CPU) used inside a microcontroller can vary widely. In many products, such as microwave ovens, the demand on the CPU is fairly low and price is an important consideration. In these cases, manufacturers turn to dedicated microcontroller chips--semiconductors designed to be small, low-cost, low-power, embedded CPUs that are combined with other components in one package. By today’s standards, microcontrollers are not the most complex chips; but they are extremely inexpensive when purchased in large quantities, and can often meet the needs of a design engineer with just one semiconductor.
The average consumer uses more than 100 microcontroller-enhanced products every day – from the thermostat in the morning, to the copier and phone at work, to the remote control for evening television viewing. While we may not notice them, microcontrollers are practically everywhere and provide direct benefits to our daily lives.
Much like tools in a hardware store, microcontrollers come in many flavors and varieties, including various packages, pin counts and memory sizes. Depending on the power and features that are needed, a design engineer might choose a 4-bit, 8-bit, 16-bit or 32-bit microcontroller. (photo source: Microchip Technology Inc.)
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