Latest Technical Details About Embedded

A microcontroller is a computer with most of the necessary support chips
onboard. All computers have several things in common, namely:
. A central processing unit (CPU) that ‘executes’ programs.
. Some random-access memory (RAM) where it can store data that is variable.
. Some read only memory (ROM) where programs to be executed can be stored.
. Input and output (I/O) devices that enable communication to be established
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:
. ‘Embedded’ inside some other device (often a consumer product) so that
they can control the features or actions of the product. Another name for a
microcontroller is therefore an ‘embedded controller’.
. Dedicated to one task and run one specific program. The program is stored
in ROM and generally does not change.
. A low-power device. A battery-operated microcontroller might consume as
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.
In this book the authors will introduce the reader to some of the Philips’ 8051
family of microcontrollers, and show their working, with applications,
throughout the book. The programming of these devices is the same and,
depending on type of device chosen, functionality of each device is determined
by the hardware devices onboard the chosen device.