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What calculator do you use ?
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McBryce:
Still using the same Sharp EL-512 that I got when I was in school (80's).

http://mycalcdb.free.fr/main.php?l=0&id=4330

McBryce.
tomlut:
Another vote for the HP42s. I have a real one as well as an emulator on my phone and my PC.

It is fast (the later HP graphical calculators were dog slow), it has just the right level of automation and features for engineering calculations.

Free HP42s emulator: http://thomasokken.com/free42/

VK3DRB:
I opened up my 1976 calculator to fix a dodgy keyboard contact.  I found this this chip: A Rockwell A4001PC.

I cannot find any data on it on the web. I would love to know what goes on inside, what algorithms it used. Rockwell is useless... they have no data on a chip they produced in 1975. One reason to keep old databooks.

If anyone has a datasheet on this chip from an old Rockwell book. I would very much appreciate it.

From what I can gather, it is designed to drive the low level VFD display, does all the normal and trigonometric functions and key board decoding and probably de-bouncing.

SeanB:
Made by Rockwell for many different manufacturers, including Casio, Olympia and others who were after a basic calculator. As you say, basically does everything including keyboard ( using the digit drives as scan lines), display driving and contains a 4 bit 4004 core, some ROM ( IIRC 8k), around 128 bytes of register ( shared RAM, stack and register space) and a high voltage ( 40V process) NMOS design, to do the display driving. Only thing it needs are a external set of supplies, -20V for the display and substrate bias, and around 6V for the logic, all provided by the DC/DC converter spread on the left side of the board.

Sorry, not in any of my databooks, but you might look at calaculatormuseum for other models using the same chip and see if you get any joy, though they were a mask ROM with slightly different code for each model, though in most cases the only difference in models was the extra keys being installed in the unit to provide the functions. You might want to look up how HP did the original HP calculators, they used a chipset that was second sourced by Rockwell and later consolidated into the single chip used here. Similar methods used for the operations in all of them.
VK3DRB:

--- Quote from: SeanB on August 09, 2015, 11:23:09 am ---Made by Rockwell for many different manufacturers...

--- End quote ---

Thanks! Very interesting info. I looked up the Intel 4004. The world's first microprocessor. Developed in 1971. This calculator was built in 1975, although the A4004PC was developed in 1973. A brilliant little chip with PROM on it, no external XTAL either. It appears the source code is non existent. It would be lovely to find that.

In those days, calculators had a wow factor. Even in uni we all had fun with our calculators. THey were like jewelry, to be admired. I preferred TI, rather than HP, but around 1977 some terrific calculators were born by these companies and they cost a mint.

These days no-one cares how a calculator works, especially the mobile phone gamer kiddies. No wow factor in it for them.

My calculator is 40 years old. The 2,300 transistors in the micro are still working strong. The capacitors are still OK.
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