Prehistory of my homemade PERSEUS computers

I will present my early homemade computers around 1980 that was the starting point for the computer project I have already introduced.

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I have described the PERSEUS series of home-built computers (PERSEUS-3, PERSEUS-7, and PERSEUS-8) from 2007 to the present in my project, but here I will describe my earlier work from the late 1970s through the 1980s. These computers are the starting point for my more recent computer and software projects.

1.    PERSEUS-68

When I was 16 years old and personal computers did not yet exist in the world, I was determined to complete a computer on my own by 1980, when I would have turned 20. The computer I built in 1980 to achieve this goal was the PERSEUS-68. The appearance of this computer is shown in Fig. 1. The CPU is a Motorola MC6802 with a system clock of 1 MHz. The RAM (MC6810) with a capacity of 128 bytes mounted on the board in addition to 128-byte CPU built-in RAM. The enclosure is made of aluminum angle, and it also serves as a card rack for the printed circuit board. The board is a universal board and wiring was done by soldering.

    Programming is a DMA method that stops the CPU and releases the bus. This is based on an article in the book [1]. Address and data are set in binary by toggle switches on the panel, and data is written to the RAM when the write switch is pressed. The address bus is 16 bits, of which the lower 8 bits are set on the panel and the upper 8 bits are set with the DIP switches on the board on the side of the chassis. In addition to normal program execution, single-step operation can be performed by pressing the switch.

Fig. 1    PERSEUS-68

    After this, I was able to complete the hardware testing of a serial interface board with expansion memory and a video interface board for character display, that I built myself to add to the card slots. However, there was an inconvenience with this computer. It did not have a function to display the execution address during single-step execution. This made it difficult to debug the program because I could not see whether the instruction execution was progressing correctly or not. Therefore, I was only able to run software on this computer, such as a machine language test program of a few dozen bytes. After PERSEUS-3 in 2007, I have installed LEDs that displays the execution address in binary when a single-step is executed.

2.    PERSEUS-88

I built this PERSEUS-88 myself in 1982. Figures 2 and 3 show the appearance of this computer. The CPU was a Fujitsu MB8870 running at 1 MHz system clock. This CPU has some instruction extensions to the MC6800. Four HM6116 SRAMs were mounted to make 8kB.

    This PERSEUS-88 does not have DMA programming and single-step execution capabilities. The computer was operated by using a monitor program called MIKBUG contained in the MC6846 from a serial terminal. The dump list of the floating-point BASIC interpreter for the 6800 that was published in a magazine was typed into the serial terminal and it was able to operate it. Data was saved and loaded by connecting a cassette tape recorder to the audio interface.

    An EPSON MP-80 dot impact printer was connected to the parallel interface. The single character output routine of the interpreter was modified so that all characters sent to the serial terminal are also sent to the printer when the printer output flag is detected. This flag was defined in 1 bit of the other parallel port and operated ON/OFF with a red toggle switch on the panel. The board was a universal board and wiring was done by soldering.

Fig. 2  PERSEUS-88

Fig. 3 Bottom view of PERSEUS-88

3.    Serial terminal

In 1982, a serial terminal was also built for PERSEUS-88 operation. This serial terminal GEMINI-230 is shown in Figures 4 and 5. The keyboard was a parallel interface type sold by ALPS in Japan at the time. The control of the transmit/receive buffer memory and the generation of the video synchronization signal were performed by a commercially available dedicated LSI SFF96364. The video output could display 64x16 characters on a CRT monitor. The character generator IC was made by writing font patterns on a PROM 2716. An UART IM6402 was used for serial communication. The communication standard is the current loop method of 300 bps or 1200 bps. The enclosure...

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Soldering side of CPU board of PERSEUS-68.

JPEG Image - 3.07 MB - 03/25/2024 at 00:23



CPU board of PERSEUS-68.

JPEG Image - 2.55 MB - 03/25/2024 at 00:22



Text display with VHF output of PERSEUS-68 video interface card connected to a home TV.

JPEG Image - 1.97 MB - 11/06/2023 at 06:01



Video monitor interface board of PERSEUS-68

JPEG Image - 2.61 MB - 04/19/2022 at 14:36



Video monitor interface board of PERSEUS-68

JPEG Image - 2.13 MB - 04/19/2022 at 14:33


  • 1 × MC6802 Microprocessors, Microcontrollers, DSPs / Microprocessors (MPUs)
  • 1 × MB8870 Microprocessors, Microcontrollers, DSPs / Microprocessors (MPUs)
  • 1 × R65C02 Microprocessors, Microcontrollers, DSPs / Microprocessors (MPUs)
  • 1 × MC6810 Memory ICs / Static RAM (SRAM)
  • 7 × HM6116 Memory ICs / Static RAM (SRAM)

View all 14 components

  • Prehistory of my homemade PERSEUS computers log

    Mitsuru Yamada11/06/2023 at 06:26 0 comments

    1. The article was first posted on Apr. 19, 2022.

    2. Revised on Nov. 6, 2023.

        Added a photo of character displaying of  PERSEUS-68 connected to home TV.

    3. Revised on Mar. 25, 2024.

        Added links of photos of the CPU board of PERSEUS-68 in chapter 1 of detail section.

View project log

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Dixbit wrote 12/03/2023 at 16:09 point

Although you say you were not satisfied with your early computers, I find them really impressive because at the time they were not "retro" computers, they could compete with the commercial offers of the era and you built them without all the data and tutorials easily found on the internet today. It's also satisfying to read that you decided to go back to make DIY computers after a 20 years pause and finally achieve your goals!

  Are you sure? yes | no

Mitsuru Yamada wrote 12/04/2023 at 01:14 point

Thank you for your comment. This prehistory project is important to me, not only because it allowed me to show you what I made around 1980, but also because it allowed me to look back at my own past. When I look back on the things I made when I was younger, I realize that I had a sensibility then that I cannot surpass today. This is the same as when you look at a picture you drew as a teenager now and get the impression that you don't know how you did it. I feel that people can create something rapidly from childhood to adolescence.

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Paul McClay wrote 06/12/2022 at 23:26 point

I enjoyed reading how your "way back" projects lead to more recent projects that you've shared here, and seeing that your elegant construction style goes all the way back. I'm a little puzzled by your choice of English for labels. And note that your hand lettering looks much better than Dymo tape!

  Are you sure? yes | no

Mitsuru Yamada wrote 06/13/2022 at 00:49 point

Thanks! Since I was a teenager I was also interested in art and industrial design, so I liked to handwrite letters on posters and such. I think it is important whether my own work looks like some kind of product or garbage, if something looks like garbage, it won't stay. I never thought of it at the time, but I am glad that I could introduce these to you now. I am not a native English speaker and would be happy to point out any unnatural English descriptions. Some parts are intentionally left strange.

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Paul McClay wrote 06/15/2022 at 18:24 point

I'm sorry - I didn't mean to suggest any fault with your English descriptions! I was wondering about how or why you chose to use English at all for labels - especially on your early projects which I assume predate influence from your later professional career. It's none of my business, just something that I was thinking about.

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NeoSyF wrote 06/06/2022 at 05:19 point

I made this account just to say your project is incredible, being just a little older than you were at the time I can see how special it actually is.I could never do it, not even with the internet on my side haha

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Mitsuru Yamada wrote 06/08/2022 at 09:34 point

Thanks. I have compiled this article in the hope that it will be enjoyable read for those of you who took on similar challenges in the early days of microcomputers. I introduced this article to a system engineer of the same age in my company, I was deeply moved to hear his story in youth that he actually enjoyed creating machine language programs on a similar CPU, which I had not known until now.

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Ken Yap wrote 05/14/2022 at 01:37 point

Thanks for writing up your projects' histories. Your projects are very tidy and beautiful. 👍

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Mitsuru Yamada wrote 05/14/2022 at 01:57 point

Thanks! These were stored in my hometown house for 40 years. I remember the sensibility of those days which I have now lost.

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