Mitsuru Yamada's Standalone Homebrew 6502 Computer Gets a Smart RPN Calculator Add-On
Programmed entirely using front panel flick-switches, the MOS 6502-based system now has a fully-functional calculator and numeric display.
While most don't relish a return to entering programs into a computer bit-by-bit via toggle switches, Mitsuru Yamada looks for a challenge — and found it in not only building a standalone minimal computer based on the MOS 6502 processor, but an add-on which makes it a functional calculator to boot.
"I have developed a minimal 6502 computer that can be programmed [in] machine language without PCs," Yamada writes of the original project to build the standalone system, inspired by early personal computers like the Altair 8800 — programmed manually, bit-by-bit, using toggle switches on its front panel. "The concept is the following three: Minimize the number of peripheral standard logic ICs to simplify the circuit; [Manual] single instruction execution is possible and the execution address is displayed at that time; To make the housing strong enough so that anyone other than me can easily operate it."
Built with reference to Rockwell's R65000 Microcomputer System Hardware Manual, published in August 1978 and available to read on The Internet Archive, the resulting system is fully-functional and built into a robust aluminum die-cast housing — processed using only a hand-drip and files. There's room even for a battery, giving the unit around five hours of operation per charge.
Simply watching flashing lights on the front panel wasn't enough for Yamada, however: The next step was to build an add-on numerical keypad and LED display to turn the system into a functional, if admittedly bulky, desk calculator.
"It performs the four arithmetic operations by 128 bits fixed-point binary coded decimal (BCD)," Yamada writes of the calculator, which uses reverse Polish notation (RPN). "It also includes scanning keys and controlling the LED display. It is implemented within the limits of the [computer's] memory capacity [of] 1 kbyte. The program is coded by hand assembly to 6502's instructions without PC environments and debugged with a single instruction execution of the computer."
Full details of the computer and the calculator add-on can be found on their respective project pages, though while Yamada has shared physical versions with selected friends and has released a schematic for the computer no design files or source code for the calculator have yet been published.