Sunday, August 11, 2013

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


Joanna Kurki 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.