RAM storage in early Texas Instruments calculator chips #VintageComputing #DieShot @kenshirriff

Ken Shirriff tackles reverse engineering RAM storage in early Texas Instruments calculator chips, from DRAM to CMOS:

Texas Instruments introduced the first commercial single-chip computer in 1974, combining the CPU, RAM, ROM, and I/O into one chip. This family of 4-bit processors was called the TMS1000… This microcontroller was also used in hand-held games and simple control applications such as microwave ovens. Since its software was in ROM, the TMS1000 needed to be custom-manufactured for each application, but it was inexpensive and sold for $2-$4 in quantity. It became very popular and was said to be the best-selling “computer on a chip”.

In the TMS1000, code and data even have different sizes: instructions were 8 bits and stored in a 1-kilobyte ROM, while data was 4 bits and stored in a 64×4 (256-bit) RAM. Since the space for RAM was limited, Texas Instruments developed new circuits for RAM: Dynamic RAM.

In 1978, TI began building CMOS calculator chips, starting with the TP0310 and TP0320 chips. These chips were used in calculators such as the TI-30-II.

TI also used CMOS to implement “Constant Memory™”, preserving calculator data even when the calculator was off; CMOS’s low power consumption meant that the memory could be continuously powered without draining the battery.

Read the details in Ken’s blog post here.


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