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Old 4th May 2020, 1:21 pm   #12
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 4,546
Default Re: Wireless World calculator project

I find the Digi-Cal a curious design.

With mechanical calculators, it was difficult to transfer a number from one register (set of counting wheels) to another. So it made sense to have dedicated multiplication counter, accumulator, etc registers.

With electronic calculators it's relatively easy to move numbers between registers. The idea of dedicated multilication counters,etc, makes a little less sense.

And yet the Digi-Cal is very much of the first type of design. Interestingly, at about the same time as the articles were published, Hewlett-Packard were selling desktop calculators built from TTL (OK + firmware ROMs and Intel 1103 DRAMs) which were very much of the 'general purpose processor + ROM firmware to make it a calculator' design. I am thinking of the HP9810 and HP9820 machines. The processor (including the memory interface circuitry) is about 100 TTL chips (including 7 256*4 PROMs).

If I was going to build a calculator from TTL I would certainly think more of that sort of design.
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