How did Microcontrollers evolve?

11 Jul

The situation we find ourselves today in the field of microcontrollers had its beginnings in the development
of technology of integrated circuits. This development has enabled to store hundreds of thousands of
transistors into one chip. That was a precondition for manufacture of microprocessor and the first
computers were made by adding external peripherals such as memory, input/output lines, timers and others
to it. Further increasing of package density resulted in creating an integrated circuit which contained both
processor and peripherals. That is how the first chip containing a microcomputer later known as a
microcontroller was developed.
In the year 1969, a team of Japanese engineers from BUSICOM company came to the USA with a request
that a few integrated circuits for calculators were to be designed according to their projects. The request
was set to INTEL company and Marcian Hoff was in charge of the project there. Since having been
experienced in working with a computer PDP8, he came to an idea to suggest fundamentally different
solution instead of suggested design. That solution presumed that the operation of integrated circuit was to
be determined by the program stored in the circuit itself. It meant that configuration would be simpler, but it
would require far more memory than the project proposed by Japanese engineers. After a while, even
though the Japanese engineers were trying to find an easier solution, Marcian’s idea won and the first
microprocessor was born. A major help with turning an idea into a ready-to-use product, Intel got from
Federico Faggin. Nine months after his arrival to Intel he succeeded in developing such a product from its
original concept. In 1971 Intel obtained the right to sell this integrated circuit. Before that Intel bought the
license from BUSICOM company which had no idea what a treasure it had. During that year, a
microprocessor called the 4004 appeared on the market. That was the first 4-bit microprocessor with the
speed of 6000 operations per second. Not long after that, American company CTC requested from Intel and
Texas Instruments to manufacture 8-bit microprocessor to be applied in terminals. Even though CTC gave
up this project at last, Intel and Texas Instruments kept working on the microprocessor and in April 1972 the first 8-bit microprocessor called the 8008 appeared on the market. It was able to address 16Kb of
memory, had 45 instructions and the speed of 300,000 operations per second. That microprocessor was the
predecessor of all today’s microprocessors. Intel kept on developing it and in April 1974 it launched 8-bit
processor called the 8080. It was able to address 64Kb of memory, had 75 instructions and initial price was
In another American company called Motorola, they quickly realized what was going on, so they launched
8-bit microprocessor 6800. Chief constructor was Chuck Peddle. Apart from the processor itself, Motorola
was the first company that also manufactured other peripherals such as 6820 and 6850. At that time many
companies recognized greater importance of microprocessors and began their own development. Chuck
Peddle left Motorola to join MOS Technology and kept working intensively on developing
At the WESCON exhibition in the USA in 1975, a crucial event in the history of the microprocessors took
place. MOS Technology announced that it was selling processors 6501 and 6502 at $25 each, which
interested customers could purchase immediately. That was such sensation that many thought it was a kind
of fraud, considering that competing companies were selling the 8080 and 6800 at $179 each. On the first
day of exhibit, in response to the competitor, both Motorola and Intel cut the prices of their microprocessors
to $69.95. Motorola accused MOS Technology and Chuck Peddle of plagiarizing the protected 6800.
Because of that, MOS Technology gave up further manufacture of the 6501, but kept manufacturing the
6502. It was 8-bit microprocessor with 56 instructions and ability to directly address 64Kb of memory. Due
to low price, 6502 became very popular so it was installed into computers such as KIM-1, Apple I, Apple
II, Atari, Commodore, Acorn, Oric, Galeb, Orao, Ultra and many others. Soon appeared several companies
manufacturing the 6502 (Rockwell, Sznertek, GTE, NCR, Ricoh, Commodore took over MOS
Technology). In the year of its prosperity 1982, this processor was being sold at a rate of 15 million
processors per year!
Other companies did not want to give up either. Frederico Faggin left Intel and started his own company
Zilog Inc. In 1976 Zilog announced the Z80. When designing this microprocessor Faggin made the crucial
decision. Having been familiar with the fact that for 8080 had already been developed he realized that many
would remain loyal to that processor because of great expenditure which rewriting of all the programs
would result in. Accordingly he decided that a new processor had to be compatible with the 8080, i.e. it had
to be able to perform all the programs written for the 8080. Apart from that, many other features have been
added so that the Z80 was the most powerful microprocessor at that time. It was able to directly address
64Kb of memory, had 176 instructions, a large number of registers, built in option for refreshing dynamic
RAM memory, single power supply, greater operating speed etc. The Z80 was a great success and
everybody replaced the 8080 by the Z80. Certainly the Z80 was commercially the most successful 8-bit
microprocessor at that time. Besides Zilog, other new manufacturers such as Mostek, NEC, SHARP and
SGS appeared soon. The Z80 was the heart of many computers such as: Spectrum, Partner, TRS703, Z-3
and Galaxy.
In 1976 Intel came up with an upgraded version of 8-bit microprocessor called the 8085. However, the Z80
was so much better that Intel lost the battle. Even though a few more microprocessors appeared later on the
market (6809, 2650, SC/MP etc.), everything was actually decided. There were no such great improvements
which could make manufacturers to change their mind, so the 6502 and Z80 along with the 6800 remained
chief representatives of the 8-bit microprocessors of that time.

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Posted by on July 11, 2010 in Microcontrollers


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