OT: Simulating a TI calculator with crazy 11-bit opcodes




That's quite awesome, thanks for the link :)


thanks for the link


Making a scientific calculator from this chip

The most amazing thing about this chip is that the Sinclair company took this chip with barely enough ROM to do four-function math, and reprogrammed it into a scientific calculator with trig, inverse trig, exponentials, and logs. The resulting Sinclair Scientific calculator became popular due to its low cost.

How did Sinclair fit all this into 320 words of ROM? The short answer is they used RPN which simplified the code, and they made extreme tradeoffs in the scientific algorithms that reduced accuracy and performance. The algorithms are a bit like decimal CORDIC, but much simplified. I plan to provide full details later.

Let's hope that ROM is available as well. That might be nice to have this calculator emulated as well.




A TI 57 is a 13 bit opcode machine :)

See patents: 4125901 4125867 4107781 4079459 for a rom dump

For testing, get go57c on google play or TI-57E from hrastprogrammer for hp 48/49

You can even use TI-57E on go48gx and go49g.

The HP50 version of TI-57E doesn't works well on go49gp (certainly some remaining bugs on go49gp)

Edited: 12 Aug 2013, 8:07 a.m.


Hi Olivier

FYI, John McMaster has hi-res photos of the TI-57 chip: see
http://siliconpr0n.org/archive/doku.php?id=mcmaster:ti:tmc1501nc and http://siliconpr0n.org/map/ti/tmc1501nc/top_metal_mit20x/

I note that HrastProgrammer fixed a few bytes in his emulator, as compared to the patent. Did you make all the same fixes? Most are OCR errors but at least a couple are not.

Here are the differences between the microcode in the patent and that in the windows simulator:

25:   1abc   1a8c
91: 1aSd 1a8d
487: 19822 1982
521: 0e07 0eff
522: 0e07 0e0d
536: 0cbd 0eff
591: 07eb 07e8
641: 1abc 1a8c
646: 17b0 1780
648: 1abf 1a8f
707: 0bc7 08c7



Yes I corrected some words. Some due to OCR, but other to restore the RST behavior of the real 57 (the listing in the patent did not have the same behavior on RST command).

A new opcode was also added to allow a light sleep mode for the emulation (to avoid consuming too much batterie)



This is a very interesting site. Thanks for its citation. After I bought my first calculator in 1972 (Bomar 901B, $130), I was intrigued by this sort of detail hidden within even simple machines.

The simulated calculator seems to stop functioning after a division by zero...the display no longer updates.


This is a very interesting site.

Yeah it really is. The 8085 ALU was a very interesting read as well.

The simulated calculator seems to stop functioning after a division by zero...the display no longer updates.

I wonder what the real thing did.

Another bug. Generate an overflow e.g. 1000 * = = and it endlessly loops at the .OVF label.

- Pauli

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