Busicom 120DN

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It happened in the beginnig of the year 1971: "The winner hit the line!" The semiconductor manufacturer MOSTEK presented the first single-chip calculator. As it is shown on the internal picture, a lot of paraphernalia is needed to complete the calculator.

This calculator was not the first, which was equipped with the MK 6010. Before, Busicom built the little bigger Busicom Junior, which contained two boards with together 22 ICs. In the middle of the run both boards were replaced by only one, which was designed in the way that nothing had to be changed: neither at the keyboard, nor at power supply nor at the display.

Circuit board

Printed circuit board of the Busicom 120

As one can see, there is a lot of "accessories" needed to complete the single-chip calculator. Above the display the power supply is located. Below the display, the five black boxes are the display drivers, left above the MK 6010 is the clock generator. The ceramic capacitors on the left of the IC are used to debounce the keyboard.

The IC in detail

The expensive chip is soldered directly, eventually because at that time there were no reliable 40-pin sockets available. But to remove it simply for testing or repair, the small pcb on which it is located, has an extra connector to the main board.

Details of the MK 6010

Interesting the japanese date which is stamped on the keramic body: 46.6.-6. The japanese counted years from the inauguration of their emperor. Emperor Hirohito (1901* 1989+) was crowned in the year 1926. That means, that the IC was stamped on may, 6th 1972, even it was fabricated in the 13th week of 1971. Also intersting the logo obove the MOSTEK sign. It is a little bit inclined, because it was added later. "NCM" stands for Nippon Calculating Machine Co.Ltd., the mother company of busicom.