Introduction

History
It was year 1969, and a team of Japanese engineers from the BUSICOM company arrived to
United States with a request that a few integrated circuits for calculators be made using their
projects. The proposition was set to INTEL, and Marcian Hoff was responsible for the project.



Since he was the one who has had experience in working with a computer (PC) PDP8, it occured
to him to suggest a fundamentally different solution instead of the suggested construction. This
solution presumed that the function of the integrated circuit is determined by a program stored
in it. That meant that configuration would be more simple, but that it would require far more
memory than the project that was proposed by Japanese engineers would require. After a
while, though Japanese engineers tried finding an easier solution, Marcian's idea won, and the
first microprocessor was born. In transforming an idea into a ready made product , Frederico
Faggin was a major help to INTEL. He transferred to INTEL, and in only 9 months had
succeeded in making a product from its first conception. INTEL obtained the rights to sell this
integral block in 1971. First, they bought the license from the BUSICOM company who had no
idea what treasure they had. During that year, there appeared on the market a microprocessor
called 4004. That was the first 4-bit microprocessor with the speed of 6 000 operations per
second. Not long after that, American company CTC requested from INTEL and Texas
Instruments to make an 8-bit microprocessor for use in terminals. Even though CTC gave up
this idea in the end, Intel and Texas Instruments kept working on the microprocessor and in
April of 1972, first 8-bit microprocessor appeard on the market under a name 8008. It was able
to address 16Kb of memory, and it had 45 instructions and the speed of 300 000 operations per
second. That microprocessor was the predecessor of all today's microprocessors. Intel kept
their developments up in April of 1974, and they put on the market the 8-bit processor under a
name 8080 which was able to address 64Kb of memory, and which had 75 instructions, and the
price began at $360.
In another American company Motorola, they realized quickly what was happening, so they put
out on the market an 8-bit microprocessor 6800. Chief constructor was Chuck Peddle, and
along with the processor itself, Motorola was the first company to make other peripherals such
as 6820 and 6850. At that time many companies recognized greater importance of
microprocessors and began their own developments. Chuck Peddle leaved Motorola to join MOS
Technology and kept working intensively on developing microprocessors.
At the WESCON exhibit in United States in 1975, a critical event took place in the history of
microprocessors. The MOS Technology announced it was marketing microprocessors 6501 and
6502 at $25 each, which buyers could purchase immediately. This was so sensational that
many thought it was some kind of a scam, considering that competitors were selling 8080 and
6800 at $179 each. As an answer to its competitor, both Intel and Motorola lowered their prices
on the first day of the exhibit down to $69.95 per microprocessor. Motorola quickly brought suit
against MOS Technology and Chuck Peddle for copying the protected 6800. MOS Technology
stopped making 6501, but kept producing 6502. The 6502 was a 8-bit microprocessor with 56
instructions and a capability of directly addressing 64Kb of memory. Due to low cost , 6502
becomes very popular, so it was installed into computers such as: KIM-1, Apple I, Apple II,
Atari, Comodore, Acorn, Oric, Galeb, Orao, Ultra, and many others. Soon appeared several
makers of 6502 (Rockwell, Sznertek, GTE, NCR, Ricoh, and Comodore takes over MOS
Technology) which was at the time of its prosperity sold at a rate of 15 million processors a
year!
Others were not giving up though. Frederico Faggin leaves Intel, and starts his own Zilog Inc.
In 1976 Zilog announced the Z80. During the making of this microprocessor, Faggin made a
pivotal decision. Knowing that a great deal of programs have been already developed for 8080,
Faggin realized that many would stay faithful to that microprocessor because of great
expenditure which redoing of all of the programs would result in. Thus he decided that a new
processor had to be compatible with 8080, or that it had to be capable of performing all of the
programs which had already been written for 8080. Beside these characteristics, many new
ones have been added, so that Z80 was a very powerful microprocessor in its time. It was able
to address directly 64 Kb of memory, it had 176 instructions, a large number of registers, a built in option for refreshing the dynamic RAM memory, single-supply, greater speed of work
etc. Z80 was a great success and everybody converted from 8080 to Z80. It could be said that
Z80 was without a doubt commercially most successful 8-bit microprocessor of that time.
Besides Zilog, other new manufacturers like Mostek, NEC, SHARP, and SGS also appeared. Z80
was the heart of many computers like Spectrum, Partner, TRS703, Z-3 .
In 1976, Intel came up with an improved version of 8-bit microprocessor named 8085.
However, Z80 was so much better that Intel soon lost the battle. Altough a few more
processors appeared on the market (6809, 2650, SC/MP etc.), everything was actually already
decided. There weren't any more great improvements to make manufacturers convert to
something new, so 6502 and Z80 along with 6800 remained as main representatives of the 8-
bit microprocessors of that time.

    
Microprocessors and microcontrollers
The first microprocessors appeared in the 1970s. These were amazing devices, which for the first time
put a computer CPU onto a single IC. For the first time, significant processing power was available at
rather low cost, in comparatively small space. At first, all other functions, like memory and input/output
interfacing, were outside the microprocessor, and a working system still had to be made of a good number
of ICs. Gradually, the microprocessor became more self-contained, with the possibility, for example, of
including different memory types on the same chip as the CPU. At the same time, the CPU was becoming
more powerful and faster, and moved rapidly from 8-bit to 16- and 32-bit devices. The development of the
microprocessor led very directly to applications like the personal computer.

Microprocessors
The first microprocessors appeared in the 1970s. These were amazing devices, which for the first time
put a computer CPU onto a single IC. For the first time, significant processing power was available at
rather low cost, in comparatively small space. At first, all other functions, like memory and input/output
interfacing, were outside the microprocessor, and a working system still had to be made of a good number
of ICs. Gradually, the microprocessor became more self-contained, with the possibility, for example, of
including different memory types on the same chip as the CPU. At the same time, the CPU was becoming.

more powerful and faster, and moved rapidly from 8-bit to 16- and 32-bit devices. The development of the
microprocessor led very directly to applications like the personal computer.

  

Microcontrollers
While people quickly recognised and exploited the computing power of the microprocessor, they also saw
another use for them, and that was in control. Designers started putting microprocessors into all sorts of
products that had nothing to do with computing, like the fridge or the car door that we have just seen.
Here the need was not necessarily for high computational power, or huge quantities of memory, or very
high speed. A special category of microprocessor emerged that was intended for control activities, not for
crunching big numbers. After a while this type of microprocessor gained an identity of its own, and became
called a microcontroller. The microcontroller took over the role of the embedded computer in embedded
systems.
So what distinguishes a microcontroller from a microprocessor? Like a microprocessor, a microcontroller
needs to be able to compute, although not necessarily with big numbers. But it has other needs as well.
Primarily, it must have excellent input/output capability, for example so that it can interface directly with
the ins and outs of the fridge or the car door. Because many embedded systems are both size and cost
conscious, it must be small, self-contained and low cost. Nor will it sit in the nice controlled environment
that a conventional computer might expect. No, the microcontroller may need to put up with the harsh
conditions of the industrial or motor car environment, and be able to operate in extremes of temperature.
A generic view of a microcontroller is shown in Figure 1.8. Essentially, it contains a simple microprocessor
core, along with all necessary data and program memory. To this it adds all the peripherals that allow it
 to do the interfacing it needs to do. These may include digital and analog input and output, or counting
and timing elements. Other more sophisticated functions are also available, which you will encounter later
in the book. Like any electronic circuit the microcontroller needs to be powered, and needs a clock signal
(which in some controllers is generated internally) to drive the internal logic circuits.


Microcontroller families
There are thousands of different microcontroller types in the world today, made by numerous different
manufacturers. All reflect in one way or another the block diagram of Figure 1.8. A manufacturer builds a
microcontroller family around a fixed microprocessor core. Different family members are created by using
the same core, combining with it different combinations of peripherals and different memory sizes. This
is shown symbolically in Figure 1.9. This manufacturer has three microcontroller families, each with its
own core. One core might be 8-bit with limited power, another 16-bit and another a sophisticated 32-bit
machine. To each core is added different combinations of peripheral and memory size, to make a number
of family members. Because the core is fixed for all members of one family, the instruction set is fixed and
users have little difficulty in moving from one family member to another.

While Figure 1.9 suggests only a few members of each family, in practice this is not the case; there can be
more than 100 microcontrollers in any one family, each one with slightly different capabilities and some
targeted at very specific applications.


Microcontroller packaging and appearance
Integrated circuits are made in a number of different forms, usually using plastic or ceramic as the packaging
material. Interconnection with the outside world is provided by the pins on the package. Where possible
microcontrollers should be made as physically small as possible, so it is worth asking: what determines
the size? Interestingly, it is not usually the size of the integrated circuit chip itself, in a conventional
microcontroller, which determines the overall size. Instead, this is set by the number of interconnection pins
provided on the IC and their spacing.
It is worth, therefore, pausing to consider what these pins carry in a microcontroller. The point has been
made that a microcontroller is usually input/output intensive. It is reasonable then to assume that a good
number of pins will be used for input/output. Power must also be supplied and an earth connection made.
It is reasonable to assume for the sort of systems we will be looking at that the microcontroller has all the
memory it needs on-chip. Therefore, it will not require the huge number of pins that earlier microprocessors
needed, simply for connecting external data and address buses. It will, however, be necessary to provide
pin interconnection to transfer program information into the memory and possibly provide extra power for
the programming process. There is then usually a need to connect a clock signal, a reset and possibly some
interrupt inputs.
Figure 1.10, which shows a selection of microprocessors and microcontrollers, demonstrates the stunning
diversity of package and size that is available. On the far right, the massive (and far from recent) 64-pin
Motorola 68000 dwarfs almost everything else. The package is a dual-in-line package (DIP), with its pins
arranged in two rows along the longer sides of the IC, the pin spacing being 0.1 inches. Because the 68000

A gathering of microprocessors and microcontrollers – old and new. From left to right: PIC 12F508, PIC
16F84A, PIC 16C72, Motorola 68HC05B16, PIC 16F877, Motorola 68000


depends on external memory, many of its pins are committed to data and address bus functions, which forces
the large size. Second from right is the comparatively recent 40-pin PIC 16F877. While this looks similar
to the 68000, it actually makes very different use of its pins. With its on-chip program and data memory
it has no need for external data or address buses. Its high pin count is now put to good use, allowing a
high number of digital input/output and other lines. In the middle is the 52-pin Motorola 68HC705. This is
in a square ceramic package, windowed to allow the on-chip EPROM (Erasable Programmable Read-Only
Memory) to be erased. The pin spacing here is 0.05 inches, so the overall IC size is considerably more
compact than the 68000, even though the pin count is still high. To the left of this is a 28-pin PIC 16C72.
Again, this has EPROM program memory and thus is also in a ceramic DIP package. On the far left is the
tiny 8-pin surface-mounted PIC 12F508 and to the right of this is an 18-pin PIC 16F84A.