Retro DIY computer project

Previously I made 4-bit CPU, and I would like to follow the progress of human being.

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I have no intension to compete with someone, nor proud of any superiority. (Actually competing by ancient 8-bit for something is non-sense. )
This project is NOT my job nor work but just joy. Shall we just enjoy it ?

Even though I've made lots AVR based BASIC computer, I still had a missing ring between CPU and computer system. This time I made a 6809, 8-bit masterpiece based BASIC computer consisting just 5 components. Indeed, this circuit and ROM image is NOT my original but reproduction of Grant's 6809 computer
The author does not allow any reproduction on the net without permission, and I have already got one. Please have respect for the orignal author (Grant), and I would thank original auth

Again I would like to write this circuit and ROM image is NOT my original. Just I made PCB files (Eagle files) and will show some fundamentals of how to write EPROM..

Before making, please read Grant's 6-chip 6809 computer carefully!!

The software, BASIC should be contained in UV-EPROM. Actually I had no experience of making something by UV-EPROM. (I have one just for duplicate something..)

The pre-owned programmer does not support modern OS (supports only before windows 7) and this time I bought this tiny programmer, TL866. This programmer is very universal and supporting not only EPROM but also PIC, Atmel AVR even DIP ATMega1284P !! very useful one.

After setting USB driver, ROM image released on Grant's homepage can be loaded by specifying start address:0C000. The released ROM mapping corresponds to memory map and BASIC part starts from 0C000.

After loading, you will see bunch of FF. The beginning part is still empty and we can add another function init.

BASIC part starts from 1B00 and,,,,

BASIC ends at 3ED6.

The very end of ROM (3FF0 to 3FFF), these byte will be found.

This programmer supports various writing voltage (up to 21 V), and NMOS type is also supported. Please refer data sheet and choose correct voltage.

Choosing "program" will show this windows. just press "Program" will write BASIC ROM.

And this is the completed BASIC computer. 5V (VCC) is taken from USB-TTL (where 5V has direct connection to USB bus voltage) but also I added two pin VCC terminal (left of serial interface)

PCB files are released on github and actual operation can be found in the following movie.

Have fun!

  • 1 × 6809 famous CPU by Motorola
  • 1 × 6850 ACIA
  • 1 × 62256 256kbit=32kB SRAM
  • 1 × 27128 16kB EP-ROM
  • 1 × 7400 Electronic Components / Misc. Electronic Components

View all 7 components

  • Tindie kit preparation on going..!

    kodera2t09/25/2016 at 09:43 2 comments

    I am not sure there are demands, but kit preparation is on going..

    Now full assembled Z80 single board computer is sold at my tindie store. It is limited number and don't miss it if some interest!

  • Now it is born. Single Board Z80 computer

    kodera2t09/21/2016 at 04:47 0 comments

    Now it is born, the single board Z80 computer. The schematic is exactly the same as my previous one, just using PCB service. It has 32kB SRAM on-board (below EP-ROM).

    The main chip is wonderful TMPZ84C015, it is highly composite CPU including two PIO, two SIO, and CTC. The board size is small but it includes,

    (1) Z80 CPU

    (2) Z80-CTC

    (3) two Z80-PIO

    (4) two Z80-SIO

    (5) Z80-CGC

    , and watchdog time just in one chip!!

    In my previous board, none of these pins are wired but this board all of functions are accessible. As same as another project, I will send this board as semi-kit at I've purchased around 10 MCUs but I need several preparations (EP-ROM writing, LPC810 firmware writing) and hopefully in a few weeks, it will be on sale. Actual operation can be found in the following movie... Stay tune!

  • New version?

    kodera2t09/19/2016 at 13:01 2 comments

    Details will be summarised soon. Stay tune!

  • Old-fashioned tiny monochrome CRT for retro computer

    kodera2t06/26/2016 at 02:09 0 comments

    I got a junk camera surveillance component just by 300JPY. Indeed I had no information of it (just only logo "Kumahira") but I eventually got the connection pinout of this tiny CRT monitor.

    It is tiny but surely Cathode-Ray-Tube, meaning B voltage should be more than 1000 V. I don't prefer high voltage (my policy is less than plus/minus 15V, if more than that, thet is out of my scope) but careful circuit trace provides which is video-in and which is Vcc....

  • Tiny LiteBSD system by PIC32MZ

    kodera2t02/27/2016 at 09:36 2 comments

    I always love full self-contained system, including data input/display console. This time I made "just a combination" system consisting of well-done circuits.

    The main board is PIC32-HMZ144 by Olimex, which has PIC32MZ2048, with 512 kB RAM and 2MB flash with micro SD card connector. The compiled ready-made binary of LiteBSD can be downloaded from this site. At the installation process, I just encounter one problem that my Pickit 3 does not support console binary upload by pic32prog (does not appear by /deb/tty.** or COM ports), and I utilised mplab_ipe, which is released by Microchip.

    It should be possible that direct USB and video handling by PIC32MZ itself but this time I just use "keyboard and video interface" designed by famous Grant, I just before made its PCB and their gerber is released here.

    Just connecting TX and RX and GND will be enough to make a complete system, fortunately bit rate of Grant's system and LiteBSD on Olimex board are same (115200). Now it is working as a "full LiteBSD" system and actual operation can be found in the following movie... have fun!

  • Again Z80 project: single board computer

    kodera2t12/29/2015 at 01:17 3 comments

    Previously I made (or just wiring?) Z80 computer consisting of AKI-80 (TMPZ84C015 based board controller) and LPC810 video console. This time I combined these two board just in one!

    Actually Toshiba TMPZ84C015 is already obsolete and I got this chip by de-soldering on AKI-80 (I got four additional dead-stocks of AKI-80 so one of them is sacrificed (or re-born as this computer)). You will see TMPZ84C015 and EPROM and may wonder where is SRAM (main memory), actually is is below EEPROM using surface mount chip.

    Indeed operation is exactly the same. but configuration is simpler than before. As you see, battery is enough to drive this self-consisting computer. I am not sure someone will try this computer but already uploaded Eagle files at github. My PCB pattern has several jumpers and please find it and not forget to connect them, if trying... Actual operation can be found in the following movie... have fun!

  • Eventually my explore reaching 32bit world!

    kodera2t12/12/2015 at 02:29 3 comments

    Eventually my explore reaching to 32bit Linux world, consisting of 68008 (32bit architecture but 8bit memory address) runs uClinux!

    Indeed this board is duplicate of 68Katy, but I had to make FTDI (FT245RL USB- parallel), which was sold by Sparkfun but now out of production, and SRAM (DIP was not available). Actual operation can be found in the following movie.. Have fun!

  • 8bit big three are explored!

    kodera2t12/05/2015 at 09:40 0 comments

    Now I made second single board computer made of "very famous" 6502!

    Indeed, also this time simply made PCB of Grant's 6502 computer.

    With the intelligent serial console, it is surely working..!

    As same as previous case, PCB files are released at github. (I am not sure someone may make PCB by the released Eagle files but if you will try, please find jumpers and wire it for fabrication.) Have fun!

  • Very intelligent video/keyboard console

    kodera2t12/05/2015 at 03:39 5 comments

    Just connecting by Retro computers via FTDI to compute (OS X or windows) we can confirm its operation but always I love "self-sufficiency system". (Indeed (I think), sending command from 21st century sophisticated monster level computer to 80's retro computer is funny..)

    Before making this very intelligent console, I quickly tried "6809 computer with video and keyboard" by LPC810 simple console by boost-up baud rate to 115.2 kbps...

    BUT, this tiny console does not have data flow control which is indispensable for high speed serial such as 115.2kbps of Grant's design. As a result, this simple LPC810 console frequently drops character and did not work well.

    On the Grant's home page, he already designed very intelligent keyboard/video interface with 115.2kbps with flow control. He realises it on bread board, but I am not so good at bread board handling, and this time I made it by PCB with SMT components.

    As well described in Grant's page, Video console is made of ATMega328 and keyboard part is by ATMega88. Initially I thought ATMega8 and 88 are compatible, but confirmed not and ordered at digikey. For firmware upload, I added ICSP terminals and put small modification to the original circuit (RST of 328 and 88 are pulled-up, not direct connection to VCC).

    After soldering, firmware can be easily uploaded by Atmel ICE.

    As well recognised, all AVR requires FUSE bit setting. Roughly explained in Grant's home page but exact ones are as follows.

    Fuse bit setting and firmware (binary) uploading can be done by ATmel Studio. This is the case of ATmega328P, as you already know, never un-set SPIEN.

    And this is the case of ATmega88.

    After setting FUSE, appropriate binary (firmware) can be uploaded through ATmel Studio..

    My PCB files are uploaded to github. My PCB assumes I2C connection between ATmega328P and ATmega88. Please find "yellow lines", which requires jumper on board. Actually this intelligent console has graphic function but at this moment I do not fully utilise. Initial character size on video is too small for small screen and its size can be modified just by sending commend

    PRINT CHR$(24); "6"
    Last "6" corresponds to font property. Details is written in Grant's home page.

    Actual operation can be found in the following movie.. have fun!

  • BY-product: Z80 based simple computer

    kodera2t11/30/2015 at 09:49 8 comments

    This is totally by-product inside 6809 project since it is working by Z80. Here you see very simple (simplest? ) Z80 system with PS/2 keyboard and monitor support. Left board contains LPC810 working as serial console, and right one AKI-80, which I bought just by 500JPY. ( Raspberry Pi Zero comparable ?? ;-)

    "AKI-80" was sold by Akizuki denshi tusho in Akihabara (Japanese site), Tokyo in early 1990's. This board had some evolution from original AKI-80 (this board), AKI-80 gold (32kB SRAM) and Super AKI-80 (including RS-232C interface). They still sell Super AKI-80 by 4980JPY (including monitor ROM and C compiler for Z80) but this time I got "dead stock" of original AKI-80 just by 500JPY. They already stopped sales of non-super AKI-80 but full information (Japanese) still can be found at their site.

    My board was just "board" and without any additional parts (X'tal, capacitors, auto reset IC) and I put several modifications (so not auto-reset)

    This Z80 is not simple surface mount package but...

    IT IS Highly integrated version of Z80 (TOSHIBA TMPZ84C015) containing Z80-SIO, PIO, CTC, and CGC just in one chip! Unfortunately this Z80 is already out-of-production but even now you can find 2nd source by Zilog at digikey. (Indeed, this is quite rare case, Zilog sells Toshiba's original product...) As a consequence of high integration, minimum computer, consisting serial I/O, can be made just with additional RAM for main memory and ROM for firmware. This time (sometimes happens to me, though), I just write EP-ROM by hex file released by great programmer (NOT ME) at ( Console is made of LPC810, this is also not my original one (information can be found at Seriously this is great masterpiece of LPC810 application!!!) and working well between PS/2 keyboard, Monitor, and AKI-80. Connection between AKI-80 and LPC810 console can be derived from this image( in this link MAX232 is connected. Instead of it, just connect with LPC810 console..) In fact, this image is a part of Japanese book and full information about this type of RETRO computer can be found by this Japanese book, written by TinyBASIC author of above link.

    Actual operation can be found in the following movie.. I would thank all the original authors for releasing their great works on the web. Have fun!

View all 10 project logs

Enjoy this project?



Hacker404 wrote 08/31/2017 at 04:30 point

Love this project.

Are you going to release the code for the LPC, that's a total gem. It would be nice to add a mouse as well.

  Are you sure? yes | no

kodera2t wrote 08/31/2017 at 04:38 point


This part (LPC810 console) is not made by me but simply utilize the code of

The source can be downloaded at

  Are you sure? yes | no

Dylan Brophy wrote 08/29/2017 at 23:51 point

Nooooo....  I went on tindie today specifically to check out this computer, as I had seen it before, only to discover that it is a retired product!  Dang!

  Are you sure? yes | no

kodera2t wrote 08/30/2017 at 13:15 point

Sorry for that. I may make "new version". Please wait a bit more..

  Are you sure? yes | no

Dylan Brophy wrote 08/30/2017 at 22:10 point

I will.  :D.  I want to test code on it because my hand soldered computer can be glitchy sometimes.  The reviews look great btw, from what I remember, so congratulations. 

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etdaron wrote 06/19/2017 at 19:12 point

Muito bom !

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Roman wrote 02/27/2016 at 14:51 point

Well, prototyping is most fun. Most of the time a prototype is all you need.

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Roman wrote 02/27/2016 at 13:54 point

Very nice project, I am just curious how do you make those boards?

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kodera2t wrote 02/27/2016 at 14:01 point

Hello, actually those are made through Eagle -> CNC -> hand soldering.. In my case, prototype is everything (no production) and that is enough for me..

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Mark wrote 02/21/2017 at 14:02 point

Could you please elaborate? Did you mill, etch or use a different method to craft the clad prototype boards? Either way, that's some fine high pitch work!

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Yann Guidon / YGDES wrote 12/06/2015 at 15:19 point

Damnit ! I already skulled this project... it's still delivering :-)

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Mike Maluk wrote 11/23/2015 at 06:29 point

Beautiful milling on the boards, very impressive!

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kodera2t wrote 11/23/2015 at 06:52 point

Thank you! I don't mention it but it is rare to complete PCB by one shot..

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Yann Guidon / YGDES wrote 11/21/2015 at 08:34 point

That's the kind of thing I wanted to build as a young teenager... there was no Internet, only scarce bibliography, expensive parts and not even an EPROM programer... This brings so many memories I thought were forgotten :-D

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kodera2t wrote 11/21/2015 at 11:26 point

Exactly! Me too, actually. In those days, book and magazine introducing single board computer, running BASIC was a dream illustrated book...

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Xark wrote 11/21/2015 at 07:20 point

Very nice!  I have some chips (CPUs, SRAMs, I/Os), but I haven't tried to make any of Grant's simple 8-bit systems myself yet (just his FPGA designs so far).

Your PCB design looks nice too (makes it look so easy and tidy vs breadboard). :-)

  Are you sure? yes | no

kodera2t wrote 11/21/2015 at 07:30 point

Thank you so much for encouraging comment!!

Indeed, for me it took some time to handle UV-EPROM. Indeed, I did not know the difference between 27128 and 27C128 requiring difference programming voltage!!

(and more, 27C128 has lots of variation by company...)

  Are you sure? yes | no

Xark wrote 11/21/2015 at 08:00 point

Good point about the ROM.  That is cool you are using authentic UVEPROM, but I don't have any anymore (although I sure remember it - slow to erase and program).  However, I have some 28C256 parallel EEPROM parts I was hoping to be able to use.

Either that or be a bit "impure" and use a larger AVR acting like a ROM (and maybe some other I/O). :-)

  Are you sure? yes | no

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