HP started designing handhelded calculators from 1968 until the end of ‘80. I buyed an HP-42S around 1993 but it has been designed near 1986.

Here I want to focus on the chip design of the 10C series, a compact set of calculator with programming abilities but with full numeric display. The HP-15C was introduced in 1982, in the full 8bit computer era, the same year of the C/64. Later model will feature a more mature “Saturn” processor. I will describe here this chip at the best of my abilities, because it sheds a light on how custom architecture was done around end of 1979.

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