Introduction
A microcontroller is a computer with most of the necessary support chips
onboard. All computers have several things in common, namely:
with the outside world i.e. connection to devices such as keyboard, mouse,
monitors and other peripherals.
There are a number of other common characteristics that define microcontrollers.
If a computer matches a majority of these characteristics, then it can be
classified as a ‘microcontroller’. Microcontrollers may be:
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Introduction
A microcontroller is a computer with most of the necessary support chips
onboard. All computers have several things in common, namely:
with the outside world i.e. connection to devices such as keyboard, mouse,
monitors and other peripherals.
There are a number of other common characteristics that define microcontrollers.
If a computer matches a majority of these characteristics, then it can be
classified as a ‘microcontroller’. Microcontrollers may be:
they can control the features or actions of the product. Another name for a
microcontroller is therefore an ‘embedded controller’.
in ROM and generally does not change.
little as 50 milliwatts.
A microcontroller may take an input from the device it is controlling and
controls the device by sending signals to different components in the device.
A microcontroller is often small and low cost. The components may be chosen
to minimise size and to be as inexpensive as possible.
The actual processor used to implement 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 – devices that were originally designed to be
low-cost, small, low-power, embedded CPUs. The Motorola 6811 and Intel
8051 are both good examples of such chips.
A typical low-end microcontroller chip might have 1000 bytes of ROM and
20 bytes of RAM on the chip, along with eight I/O pins. In large quantities, the
cost of these chips can sometimes be just a few pence.
Microcontroller types
The predominant family of microcontrollers are 8-bit types since this word
size has proved popular for the vast majority of tasks the devices have been
required to perform. The single byte word is regarded as sufficient for most
purposes and has the advantage of easily interfacing with the variety of IC
memories and logic circuitry currently available. The serial ASCII data is also
byte sized making data communications easily compatible with the microcontroller
devices. Because the type of application for the microcontroller may vary
enormously most manufacturers provide a family of devices, each member of
the family capable of fitting neatly into the manufacturer’s requirements. This
avoids the use of a common device for all applications where some elements of
the device would not be used; such a device would be complexan d hence
expensive. The microcontroller family would have a common instruction subset
but family members differ in the amount, and type, of memory, timer facility,
port options, etc. possessed, thus producing cost-effective devices suitable for
particular manufacturing requirements. Memory expansion is possible with offchip
RAM and/or ROM; for some family members there is no on-chip ROM,
or the ROM is either electrically programmable ROM (EPROM) or electrically
erasable PROM (EEPROM) known as flash EEPROM which allows for the
program to be erased and rewritten many times. Additional on-chip facilities
could include analogue-to-digital conversion (ADC), digital-to-analogue conversion
(DAC) and analogue comparators. Some family members include
versions with lower pin count for more basic applications to minimise costs.
Many microcontroller manufacturers are competing in the market place and
rather than attempting to list all types the authors have restricted the text to
devices manufactured by one maker. This does not preclude the book from
being useful for applications involing other manufacturer’s devices; there is a
commonality among devices from various sources, and descriptions within the
text can, in most cases, be applied generally.
