Simulating a TI calculator with crazy 11-bit opcodes

I've built a register-level simulator of a 1974 TI calculator chip that shows what actually happens inside a calculator when you perform operations and shows the calculator source code as it executes. The architecture of the calculator chip is pretty interesting, with 11-bit opcodes, a 9-bit address bus, and 44-bit BCD registers. The chip doesn't support multiplication or division, so these are performed with repeated addition or subtraction.

The simulator is at


Unknown said...

Interisting info there aabout those old calculators.

Do you happen to kniw what kind of CPU the Sinclair Cambridge Programmable had? I used to have one of those (broke years ago) and would like to see emulator for it.

Ken Shirriff said...

According to Vintage Calculators, the Sinclair Cambridge Programmable uses the National Semiconductor MM5799EHY/N and DS7784N. I don't know anything about those chips. But stay tuned for more about the Sinclair Scientific.

Ed said...

Great stuff Ken!
But the linked schematic on Picasaweb is broken for me.

Anonymous said...

The link to the emulator doesn't work.

Ken Shirriff said...

Ed and anonymous: the links should work now. Thanks for letting me know.

daniel lisa said...

To convert the battery of a TI Programmable 57 calculator, follow these steps:

Identify Battery Type: The TI Programmable 57 calculator typically uses rechargeable NiCd (Nickel-Cadmium) batteries. However, if it's been modified or updated, it might use different types. Ensure you know the exact battery type.

Check Voltage Requirements: Confirm the voltage requirements of the calculator. The TI Programmable 57 generally operates on around 3.6 to 4.5 volts.

Select Replacement Batteries: Choose replacement batteries that match the voltage requirements. If NiCd batteries are preferred, select high-quality ones with the appropriate voltage rating.

Install Batteries: Remove the old batteries and insert the new ones into the battery compartment, ensuring correct polarity.

Charge if Necessary: If using rechargeable batteries, charge them fully before use to maximize performance.

As for the "Simple CGPA to Percentage Calculator," here's a simple formula to convert CGPA to percentage:

Percentage = CGPA * 9.5

This formula is commonly used in many educational institutions where the CGPA is on a scale of 10. By multiplying the CGPA by 9.5, you get the approximate percentage equivalent. For instance, a CGPA of 8.0 would convert to approximately 76%.

So, if you want to create a simple calculator for this conversion, you would input the CGPA and then multiply it by 9.5 to get the equivalent percentage.