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The single chip, using a p-channel process, replaced 22 chips in the previous version of this Busicom Junior calculator, see below, and reduced the number of circuit boards from two to one. Note that separate transistors are
still needed as high-voltage display drivers.
The article continues ... "The original calculator's discrete diode-resistor and IC logic was a very clever design, says Mostek, developed over many years and requiring nearly the minimum logic necessary for a four-function
machine. ... the minimised logic contributed greatly to Mostek's success in putting a calculator on a single chip".
Mostek of Dallas was then less than 2 years old. For more information about Mostek visit the MostekLives site.
This was the first use ever of a single chip for all the functions of a calculator, described then as a "Calculator on a Chip". It was the cutting-edge technology of the day .
This was the culmination of the gradually increasing integration during the late 1960s, accompanied by reducing number of components. Driving the display required higher power transistors which could not
be easily integrated with the logic circuits on the chip, but within a couple of years this was achieved and the only electronics required for a simple calculator was the one chip.
The reduction of the calculator logic to a single chip had two immediate effects:
- The calculator could now be much smaller and consumed much less power, leading on to small pocket calculators (eg. the Busicom Handy LE-120).
- Assembly was much simpler so low labour costs were not so important and many manufacturers appeared in the U.S.A. and Europe. A few years later, when the cost of the chip, display, and keyboard had
dramatically fallen, the assembly cost again became a large proportion of the total cost and manufacture returned to low labour-cost countries.
The development of electronics had now reached the stage at which a truly pocket-sized calculator was possible.
NCR 18-15
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