Classic Calculator Was Reverse Engineered from the Bare Metal

https://spectrum.ieee.org/geek-life/hands-on/this-classic-calculator-was-literally-reverse-engineered-from-the-bare-metal

by samizdis • 6 years ago

168 68 6 years ago

spectrum.ieee.org

samizdis2• 6 years ago

... the replica reproduced its behavior, by using an emulator running firmware that had been reverse engineered by visually examining the metal of an original processor.

barbegal3• 6 years ago

Ken Schirriff's blog has a much more detailed and interesting explanation including photos of the die that were used to reverse engineer it. http://files.righto.com/calculator/sinclair_scientific_simul...

samizdis2• 6 years ago

Excellent. Thanks for that.

leni536• 6 years ago

How can sine and cosine be computed efficiently in a calculator that has a hard time even doing multiplication? The trick is to do repeated rotations by 0.001 radians until the desired angle is reached.

Genius!

kens3• 6 years ago

Thanks. My last name is "Shirriff", by the way (no "c").

Qasaur• 6 years ago

Somewhat off-topic, but why does the IEEE (a non-profit) have annoying ads on their site? I'm not using an ad-blocker and as soon as I clicked the link I was bombarded by one big half-page ad and a bunch of other ads that are irrelevant to the content of the article.

I would have thought that their very expensive membership fees and article/publication fees would have covered their operating expenses.

metaphor• 6 years ago

To rub salt into the wound, even dues-paying regular members aren't immune to such ridiculous ad bombardment.

Yetanfou• 6 years ago

Somewhat off-topic, but why does the IEEE (a non-profit) have annoying ads on their site?

Because you forgot to install or enable an ad blocker. I know this is not a real answer to your question but it is the best answer to the annoying ads problem.

matheusmoreira• 6 years ago

I'm not using an ad-blocker

Why not? The advertising is never going to stop unless everyone blocks it. Content blockers should come pre-installed with all browsers. Ideally, they should be fully integrated features instead of mere extensions.

That's the only way for browsers to still retain their status as user agents. Browsers are supposed to act on our behalf by showing us the information we want to see. They aren't supposed to show us advertising noise for someone else's benefit.

I would have thought that their very expensive membership fees and article/publication fees would have covered their operating expenses.

It's not about covering operating expenses. Memberships revenue + advertising revenue will always be greater than memberships revenue alone. It's an easy choice for them to make. Why would they actively choose to make less money than they could be making?

This advertising noise will never disappear on its own. We need to actively get rid of it. We need to make it so that advertising is a waste of money for companies. That's the only way to make them stop.

amelius• 6 years ago

Here's someone who rebuilt the device with modern parts:

https://hackaday.io/project/91895-sinclair-scientific-calcul...

throwaway_pdp09• 6 years ago

That is one strange calculator. It's like having a car with 3 buttons; forward, backward and teleport.

Aardwolf• 6 years ago

Forward, backward and rotate left.

anewdirection• 6 years ago

If childhood taight me anything, the minimum is just 2 buttons. Forward, reverse-left. Simple, usually effective, and maddenly oversimplified. I think I liked the one that only sent forward more, but it of course required a track.

People forget simple things like steering servos were not available to most kids until the 90s injection molding explosion that is so ubiq today.

thaumasiotes3• 6 years ago

The Sinclair Scientific was able to reduce complexity by using reverse Polish notation, in which mathematical operators come after the numbers they are operating on—for instance, “5 + 4 =” becomes “5 4 +.”

This is a great example of a place where you shouldn't use punc-quote formatting. There is no . key on the calculator, but that's not obvious while you're reading the article.

zapzupnz• 6 years ago

This is a great example of a place where you shouldn't use punc-quote formatting

There's no place where it should be used. It can only introduce ambiguities, never solve any.

Quote-punc, on the other hand, doesn't introduce any. What always drove me nuts in academic writing was the knowledge that no matter how well I chose to format my article, the publisher would always introduce punc-quote and wreck things.

I'd have to defensively write around the potential placement of a punctuation mark which is just insane.

kleiba4• 6 years ago

My former boss, a university professor, is a very good writer and leaning towards the anal side when it comes to things like punctuation, wording, spelling, etc. I remember we once worked on a journal article together that was edited somewhere in India. She sent in a pristine source file, and got back a print proof where literally tens of mistakes had been introduced. She corrected them meticulously, sent the corrected version back, and received another proof with another tens of errors introduced.

This went on for quite a while, you can only admire my boss's perseverance. However, what I don't understand is how these mistakes could have been introduced in the first place? It almost felt like someone on the other end was actually retyping all of her writing, or else how was it possible to get all of these mistakes in there?

cjmb• 6 years ago

Strongly agree. When the rules are bad, don't conform to them. I always use Quote-punc in my own writing if there is any possibility of ambiguity.

apk-d• 6 years ago

Maybe my monkey programmer brain is broken already from doing syntax parsing all day, but I can never imagine any context where this formatting makes sense. I always place quotation marks "like this". The other way is not even consistent with the conventional parentheses placement (like this).

michaelcampbell• 6 years ago

While I agree with you and refuse to do it the "traditional" way, there is some interesting reading about it here: https://style.mla.org/punctuation-and-quotation-marks/

jstanley• 6 years ago

I think it makes sense to include the punctuation inside the quotes if you are quoting the punctuation, and not if you are not.

MiroF• 6 years ago

The english language is full of idiosyncrasies that don't quite make sense. Punc-quote is the correct "formal" way but informally you're free to do anything you want.

lscotte• 6 years ago

You are correct regarding the formatting, but there is "." key.

gpvos• 6 years ago

No, there is not. See the article, and https://en.wikipedia.org/wiki/File:Sinclair_Scientific.jpg

dhimes2• 6 years ago

On the HP it's

    5 ENTER 4 +

kps2• 6 years ago

On the Sinclair it is in fact

    5 + 4 +

because there is no ENTER key — the first ‘+’ is adding 5 to 0.

Mathnerd3142• 6 years ago

I found an old printer's manual a while back. The original typesetting guideline was to put the quote and the period in the same column, one above the other. This evolved to punc-quote on typewriters.

So I blame proportional fonts for their missing ligatures. :-)

paulgerhardt• 6 years ago

Oh this is delightful. Can you share the reference if you have it still?

thaumasiotes3• 6 years ago

Not at all surprising, since that's how you would do it in handwriting.

dreamcompiler• 6 years ago

Curious where you found this. I used to hand-set lead type and I don't remember any ligatures that combined quotation marks with periods.

Frost1x• 6 years ago

I would have padded the end of sentence with something else to avoid it or restructured the sentence entirely.

appleflaxen• 6 years ago

...you shouldn't use punc-quote formatting...

it seems like this is a really basic idea, but a web search is failing to explain to me what "punc-quote" formatting means. I get that it refers to how a command should be parsed, and how punctuation affects it, but can you give me a link to a formal explanation?

anyfoo2• 6 years ago

Nothing to do with parsing commands, just with writing sentences in articles (or elsewhere). It’s the difference between having punctuation that is not part of a quote in the quote, like when I said last Tuesday to “not do it like this,” or outside of them, “like this”.

The former is supposedly the “correct” way, at least in English, but you can see from my explanation that I’m absolute against it. I’m sorry, it’s just wrong on so many levels, and whoever invented it were not understanding what they were doing.

monocasa• 6 years ago

It's just how formal US English requires quite a bit of punctuation to be inside the quotes, even if the punctuation isn't being quoted.

https://blog.apastyle.org/apastyle/2011/08/punctuating-aroun...

This rule is obvs not super composable, and leads to a lot of confusion when punctuation (or lack thereof) is part of what you're trying to quote.

teddyh• 6 years ago

Hackers tend to use quotes as balanced delimiters like parentheses, much to the dismay of American editors. Thus, if “Jim is going” is a phrase, and so are “Bill runs” and “Spock groks”, then hackers generally prefer to write: “Jim is going”, “Bill runs”, and “Spock groks”. This is incorrect according to standard American usage (which would put the continuation commas and the final period inside the string quotes); however, it is counter-intuitive to hackers to mutilate literal strings with characters that don't belong in them. Given the sorts of examples that can come up in discussions of programming, American-style quoting can even be grossly misleading. When communicating command lines or small pieces of code, extra characters can be a real pain in the neck.

— http://www.catb.org/~esr/jargon/html/writing-style.html

combatentropy• 6 years ago

This is why I try to mark things with something besides quotes: like bold, italics, or monospaced (unless it's a quotation in the old sense, something that someone said). In this calculator example, the two versions might have been better in <pre> tags, setting each on its own line, like this:

The Sinclair Scientific was able to reduce complexity by using reverse Polish notation, in which mathematical operators come after the numbers they are operating on — for instance:

  5 + 4

becomes:

  5 4 +

---

The U.S. chose its quotation-mark rules for graphical reasons, not logical ones. But the graphical improvement is slight, even debatable.

I wonder if my fellow Americans even notice the difference or remember which way is right. In fact, sometimes they look at it askew. One of my Facebook posts drew criticism from my friends, who said it was hard to parse. It was a post about different words, so several were in quotes, intermixed with commas, and I had diligently followed the American style.

I have hesitated to adopt quote-punc, just as I write color instead of colour. When a difference is slight, I think it's better to follow convention --- like contributing to source code and using the indentation style already there.

But after the Facebook incident and others, including this one, I'm beginning to think the difference isn't slight. Especially in the global melting pot of the Internet, it matters less to follow your own country's convention.

fnord77• 6 years ago

I was on a VPN and was getting http 418 from this server. Weird.

drfuchs• 6 years ago

Why can't they mention "CORDIC" so that interested readers can find out the cool details about how to actually calculate "... trigonometric functions by repeatedly rotating an initial vector until the target angle was reached..." using only fixed-point add, subtract, and shift?

Someone• 6 years ago

Nitpick: this calculator uses only one of the core ideas of CORDIC: that one can compute sines and cosines by repeated rotation. It doesn’t use the other core idea that you can approximate any angle by successively halving each step.

It doesn’t do the latter because of lack of memory to implement it in. http://files.righto.com/calculator/sinclair_scientific_simul...:

“How can sine and cosine be computed efficiently in a calculator that has a hard time even doing multiplication? The trick is to do repeated rotations by 0.001 radians until the desired angle is reached.

[…]

Other calculators use algorithms such as decimal CORDIC that are much faster and more accurate, taking time proportional to the number of digits.”

roelschroeven3• 6 years ago

The Sinclair Scientific was able to reduce complexity by using reverse Polish notation, in which mathematical operators come after the numbers they are operating on—for instance, “5 + 4 =” becomes “5 4 +.”

It's not really RPN though. RPN lets you write "2 × (5+4)" as "2 5 4 + ×", but the Sinclair Scientific doesn't support that. It would have needed a stack for that, which wasn't available. Instead each operation simply acts on the previous result. You'd have to use "5 + 4 + 2 ×" instead.

Still very impressive how they managed to accomplish all that using that simple TI chip and only 320 instructions.

ec109685• 6 years ago

It’s not “5 4 + 2 x”?

morcheeba• 6 years ago

changing the order like that doesn't extend to "(5+4)*(3+2)"

duskwuff• 6 years ago

That'd give you 54 x 2. You have to press + to delimit the initial value.

thaumasiotes3• 6 years ago

Technically, you still need delimiters in RPN, so "2 5 4 + ×" won't get you anything, because it's invalid. You need "2 ENTER 5 ENTER 4 + ×"

But that is both mentally more difficult to handle and physically more difficult to input than "5 ENTER 4 + 2 ×", so I wouldn't count this as a strike against the Sinclair even theoretically.

barbegal3• 6 years ago

The patent https://patentimages.storage.googleapis.com/0d/b2/87/7f219f3... for the chip this calculator was based on (the TMS080x) is a real work of art. If you know how to make a transistor and a seven segment display, you can build yourself a fully working calculator with the information in the patent.

The architecture is truly odd, using 44 bit registers (11 x 4-bit BCD) and 11-bit opcodes. It is more like an electrical abacus than a microcontroller.

kens3• 6 years ago

Most patents are worthless for learning anything, but Texas Instruments has some remarkably useful patents. That one, in particular, is a 61-page complete description of the calculator hardware with detailed schematics, as well as the software in flowchart and assembly form and the chip's instruction set. The patent has enough information to completely simulate the calculator (which I did: http://righto.com/ti). This patent was clearly written by the engineers and not the lawyers.

The funny thing is that what the patent actually claims is an obscure technique for connecting the ground lines in the calculator's ROM. In other words, almost all the detailed text in the patent is irrelevant to what is actually patented.

barbegal3• 6 years ago

Thanks Ken, it's a great simulator. Is there any way others could write code for this simulator and play around with it as opposed to just running the original code?

And what are the best and worst features of this hardware architecture? Was there any little thing you think the designers should have done to improve it? Or was there something genius about it?

Paperweight2• 6 years ago

The UI design of calculators is fascinating. Where do you put the buttons? TI and friends have a randomish layout, let alone the TERRIBLE mobile calculator apps.

(Self-promotion) I always wanted to design a calculator and finally got around to it as a lockdown project - https://ucalc.app

ajnin• 6 years ago

OT but it's a real shame the bubble LED displays used in those calculators are not manufactured anymore. Something about the warm red glow and incandescent-like filament look appeals to me. They are also very compact, it's occasionally possible to find more recent bubble displays but quite bulkier, and outrageously expensive.

Classic Calculator Was Reverse Engineered from the Bare Metal

Related Stories