Zoltan Pekic Brings Back a Pair of Classic Pocket Calculators in FPGA Form on the MicroNova Mercury
Project features Texas Instruments Datamath and Sinclair Scientific modes, complete with a physical keypad and VGA video output.
Developer Zoltan Pekic has recreated a pair of classic 1980s pocket calculators, but with a twist. Their modern recreations are written in VHDL and run on a MicroNova Mercury field-programmable gate array (FPGA) development board.
While desk and pocket electronic calculators have largely gone the way of the mechanical calculators before them, a victim of the ubiquitous smartphone, enthusiasts not only enjoy the experience of using the vintage hardware itself but also of understanding exactly how it works — and Pekic can definitely lay claim to having a good understanding of both the Texas Instruments Datamath and Sinclair Scientific calculators, having rebuilt them in the VHDL hardware description language.
"Inspired by [Ken Shirriff's TI Datamath and Sinclair Scientific simulators] I set out to do similar in VHDL, for [the] MicroNova Mercury board," Pekic writes. "Not one, but two vintage desktop calculators rolled into a single FPGA! This VHDL implementation encapsulates both TI Datamath and Sinclair Scientific — a single input signal 'virtual pin' switches the mode.
"The 'chip' is hosted within glue logic that provides interface to the Mercury baseboard hardware (switches, buttons, 4 digit LED, VGA). The keyboard is hex PMOD, the keys change meaning if in TI or Sinclair mode. All of this is (somewhat) documented here or in the source code. The core of the implementation is 256 deep * 52 bit wide microcode routine. In a single clock cycle, a single 4-bit digit is processed, and to execute a single TMS0800 instruction, usually 12+ cycles are needed."
The result is a modern FPGA-based implementation of two classic calculators of the 1980s, complete with features not previously available including a VGA video output. There are, however, a few glitches to contend with, disclosed in Pekic's most recent project update. "Both modes are operational, but with some bugs," Pekic explains. "Time permitting I may continue fixing them and improving. I hope somebody finds this project interesting, it was tons of fun and learning, and truly fascinating journey into retro-computing!"
The full write-up is available on Pekic's project page.