Binary – the way micros count

Unlike us, microprocessors have not grown up with the idea that 10 is
a convenient number of digits to use. We have taken it so much for
granted that we have even used the word digit to mean both a finger
and a number.
Microprocessors and other digital circuits use only two digits – 0 and
1 – but why? Ideally, we would like our microprocessors to do
everything at infinite speed and never make a mistake. Error free or
high speed – which would you feel is the more important?
It’s your choice but I would go for error free every time, particularly
when driving my car with its engine management computer or when
coming in to land in a fly-by-wire aircraft. I think most people would
agree.
So let’s start by having a look at one effect of persuading microprocessors
to count in our way.
The noise problem
If the input of a microprocessor is held at a constant voltage, say 4V,
this would appear as in Figure 2.1.
If we try to do this in practice, then careful measurements would show
that the voltage is not of constant value but is continuously wandering
above and below the mean level. These random fluctuations are called
electrical noise and degrade the performance of every electronic
circuit. We can take steps to reduce the effects but preventing it
altogether is, so far, totally impossible. We can see the effect by
disconnecting the antenna of our television. The noise causes random
speckles on the screen which we call snow. The same effect causes an
audible hiss from the loudspeaker. The effect of noise is shown in
Figure 2.2.

Microprocessor-based system

This is any system that contains a microprocessor, and does not
necessarily have anything to do with computing. In fact, despite all the
hype, computers use only a small proportion of all the microprocessors
manufactured. Our garage door opening system is a
microprocessor-based system or is sometimes called a microprocessorcontrolled
system.

Microcomputer

The particular microprocessor-based systems that happen to be used
as a computer are called microcomputers. The additional circuits
required for a computer can be built into the same integrated circuit
giving rise to a single chip microcomputer.

Microcontroller

This is a complete microprocessor-based control system built onto a
single chip. It is small and convenient but doesn’t do anything that
could not be done with a microprocessor and a few additional
components. We’ll have a detailed look at these in a later chapter.

MPU and CPU

An MPU is a MicroProcessor Unit or microprocessor. A CPU is a
Central Processing Unit. This is the central ‘brain’ of a computer and
can be (usually is) made from one or more microprocessors. The IBM
design for the ‘Blue Gene’ supercomputer includes a million
processors!

Micro

The word micro is used in electronics and in science generally, to
mean ‘one-millionth’ or 1  10–6. It has also entered general language
to mean something very small like a very small processor or
microprocessor. It has also become an abbreviation for microprocessor,
microcomputer, microprocessor-based system or a micro
controller – indeed almost anything that has ‘micro’ in its name. In the
scientific sense, the word micro is represented by the Greek letter 
(mu). It was only a small step for microprocessor to become
abbreviated to P

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