TTL Calculator Project

Tony Duell ard at
Thu Dec 21 16:01:18 CST 2006

> Several months back, we talked about a calculator built from TTL.  It =
> came
> from a 1970's article in Practical Electronics, an English Magazine.

I have originals of that....

It's interesting to compare that design with the HP9810 (either from the 
patent or from the schematics on They're approximately 
contemporary (I think the 9810 came out in late 1971), they're both built 
from TTL (although the HP also has some PMOS DRAMs and MOS ROMs).

The bigest difference is the architacutre. The Digi-Cal is a calculator 
in hardware. There's a multiplication counter. A BCD full-adder. And so 

The HP is really a computer. There's a general-purpose 16 bit processor 
in there (shich. OK, has a few BCD-related isntructions). Connected to it 
is RAM and DRO, the latter contains the programs to make it work as a 
calculator. And peripherals like the keyboard, display, and printer.

That the HP is a general-purpose design is shown by the fact that the 
HP9810 (3-level stack RPN calculator), 9820 (algebraic-notation 
calculator) and 9830 (BASIC-programamble computer) are all essentially 
the same design and use the same processor boards.

> I had 7 requests for copies, which I mailed directly to the requestors.
> Apparently they disappeared into a black hole, because I didn't receive =
> a
> single acknowledgement, let alone a thank you.

That, alas, is typical.


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