Introduction to Microcontrollers

1.3. NOTATION 7
operated stand-alone, at the very least it requires some memory and an output device to be
useful.
Please note that a processor is no controller. Nevertheless, some manufacturers and vendors list
their controllers under the term “microprocessor”. In this text we use the term processor just
for the processor core (the CPU) of a microcontroller.
Microcontroller: A microcontroller already contains all components which allow it to operate standalone,
and it has been designed in particular for monitoring and/or control tasks. In consequence,
in addition to the processor it includes memory, various interface controllers, one or
more timers, an interrupt controller, and last but definitely not least general purpose I/O pins
which allow it to directly interface to its environment. Microcontrollers also include bit operations
which allow you to change one bit within a byte without touching the other bits.
Mixed-Signal Controller: This is a microcontroller which can process both digital and analog signals.
Embedded System: A major application area for microcontrollers are embedded systems. In embedded
systems, the control unit is integrated into the system 3 . As an example, think of a cell
phone, where the controller is included in the device. This is easily recognizable as an embedded
system. On the other hand, if you use a normal PC in a factory to control an assembly
line, this also meets many of the definitions of an embedded system. The same PC, however,
equipped with a normal operating system and used by the night guard to kill time is certainly
no embedded system.
Real-Time System: Controllers are frequently used in real-time systems, where the reaction to an
event has to occur within a specified time. This is true for many applications in aerospace,
railroad, or automotive areas, e.g., for brake-by-wire in cars.
Embedded Processor: This term often occurs in association with embedded systems, and the differences
to controllers are often very blurred. In general, the term “embedded processor” is used
for high-end devices (32 bits), whereas “controller” is traditionally used for low-end devices (4,
8, 16 bits). Motorola for example files its 32 bit controllers under the term “32-bit embedded
processors”.
Digital Signal Processor (DSP): Signal processors are used for applications that need to —no surprise
here— process signals. An important area of use are telecommunications, so your mobile
phone will probably contain a DSP. Such processors are designed for fast addition and multiplication,
which are the key operations for signal processing. Since tasks which call for a signal
processor may also include control functions, many vendors offer hybrid solutions which combine
a controller with a DSP on one chip, like Motorola’s DSP56800.
1.3 Notation
There are some notational conventions we will follow throughout the text. Most notations will be
explained anyway when they are first used, but here is a short overview:
3 The exact definition of what constitutes an embedded system is a matter of some dispute. Here is an example
definition of an online-encyclopaedia [Wik]:
An embedded system is a special-purpose computer system built into a larger device. An embedded system
is typically required to meet very different requirements than a general-purpose personal computer.
Other definitions allow the computer to be separate from the controlled device. All definitions have in common that the
computer/controller is designed and used for a special-purpose and cannot be used for general purpose tasks.