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Reverse-engineering an early calculator chip with four-phase logic
04-23-2023, 03:15 PM
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Reverse-engineering an early calculator chip with four-phase logic
Early integrated circuit designs are fascinating and a thing of beauty.

I came across a blog article that got my attention for the amount of detail revealed in analyzing a calculator Rockwell LSI. Rockwell four-phase PMOS LSI were used in various brands of calculators in the early 70s. This article highlights the details of one such LSI. If you're a fan of early hardware and schematics like I am, this article does not disappoint!

Decimal point control

Look for example at this beautiful design for a decimal point decoder to display the decimal point:

[Image: complex-gate.jpg]

and its schematic:

[Image: digit-gate.jpg]

Segment driver

The segment driver converts a digit to its 9 segment display output (a VFD tube):

[Image: segment-decoder.jpg]

to light segments a to i (and decimal point):

[Image: nine-segment-labeled.jpg]

Transistors, resistors, capacitors and gates

A lot of details are explained, such as the four-phase delay clock gate:

[Image: gate-diagram.jpg]

Links

Reverse-engineering an early calculator chip with four-phase logic

Reverse-engineering the clock chip in the first MOS calculator

Reverse-engineering the multiplication algorithm in the Intel 8086 processor

Reverse-engineering the division microcode in the Intel 8086 processor

The Texas Instruments TMX 1795: the (almost) first, forgotten microprocessor also features 4004, 8008, AL1, Viatron 2101, MP944 / F-14 CADC (F14 fighter flight control system), TMS 0100 calculator-on-a-chip / microcontroller

- Rob

"I count on old friends" -- HP 71B,Prime|Ti VOY200,Nspire CXII CAS|Casio fx-CG50...|Sharp PC-G850,E500,2500,1500,14xx,13xx,12xx...
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