PERSEUS-3 Is a Modern MC6802 Computer with a Gorgeous Vintage Look and Feel

Enter programs with the front panel switches, see status with the LEDs, or use RS-232C.

James Lewis
a month agoRetroTech

Mitsuru Yamada designs gorgeous 8-bit computers and peripherals with a stunning vintage visual style. One such machine is the PERSEUS-3 homebrew computer featuring a Motorola MC6802 microprocessor. This machine is not only beautiful; it is also fully functional. It even comes with its own interpreted language!

Previously, we covered Yamada's MC6802-based serial terminal with bubble LEDs and an RPN-calculator add-on for the newer 6502-based PERSEUS-7. A brief look at these projects shows they all belong to the same family.

PERSEUS-3 is an older project built with the Motorola MC6802 microprocessor. This CPU is nearly the same as the more popular MC6800 chip. One key difference is that when the MC6802 HALTs, its address bus does not go high impedance. Since the data stays persistent on the bus, PERSEUS-3's front panel LEDs can show the last used address when the CPU stops.

The memory capacity is 16 kilobytes with an interpreter using about 2 kilobytes of RAM. Instead of a dedicated ROM, a 70 mAh battery provides back-up power to the memory. For input and output, there are both digital and analog options. PERSEUS features Eight digital I/O pins buffered through a 74HCT374 chip. Unlike most vintage 8-bit computers, there is an analog-to-digital converter (ADC) and a digital-to-analog converter (DAC). Both support signals up to about 2.5 volts.

Program entry happens with sixteen address and eight data switches. Also, there is an RS-232C interface that accepts programming and provides output from the built-in interpreter.

Computation Interpreter-1 (CI-1) looks a bit like BASIC but is Yamada's original creation. It supports 16-bit integers, 26 variables (letters), four arithmetic operations, conditional statements, and jump operations. Like BASIC, if you enter an instruction with a line number, it gets added to the program listing. Otherwise, the interpreter executes the instruction immediately. Amazingly, CI-1 only needs about 1,700 bytes!

Demonstration of CI-1 running on PERSEUS-3

After building PERSEUS-3, Yamada created other computers, including the PERSEUS-7, which features a Rockwell 6502 microprocessor. You can find information about it on the PERSEUS-7 project page.

For a block diagram, schematic, and several excellent pictures of this MC6802 computer, check out the PERSEUS-3 project page.

James Lewis
Fan of making things that blink, fly, or beep. Oscilloscopes for R&S, host on element14 Presents,, AddOhms, and KN6FGY.
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