CRISS CP/M 8-bit Homebrew DIY Computer (AVR based)

the FIRST single-board DIY 8-bit personal computer with VGA, Ethernet and printer support, GPIO and CP/M powered!

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Meet my CRISS CP/M: the modern single-board 8-bit full-featured DIY personal computer! Amazing functionality for the DIY device: it is not a toy, it is REAL Computer, spy-free Computer and the sophisticated control platform for your projects!


OS: CP/M 2.2 = programming languages, text processors, games, business software, ...
Instructions: Z80 (Zilog), extended with MUL, DIV, and floating-point, 1us LD r,r ops
Memory: 64 Kb SRAM + 128 Kb EPROM = 3 switchable user sessions!
Video: VGA (!) monochrome 24/25x80 5 symb sets, graphics 160x96 px + sleep mode (!)
Storage: SD-card
Keyboard: PS/2, 2 layouts
Printer: YES, serial or LPT
Interfaces: RS-232, UART, Ethernet, GPIO
Real time clock with battery
Single-tone melody generator with built-in speaker
Hardware emulation: VT100, Robotron PC1715, Kaypro II, ADM, Microbee, TRS-80, ...

8-bit AVR MCUs based, DIP only (!), no modules and development boards, 100% open project, programmers support website

The basic idea was to build really 8-bit computer that would use modern technologies and components. CRISS CP/M did it! 8-bit MCUs only, standard keyboard, monitor and LAN can be used, CP/M OS provides compatibility with the standard software, LAN and other "modern" features are incorporated into the BIOS and accessible with just few lines of code from a user program!

Single-board design, AC/DC PSU is on the board, standard sockets, DIP components only, and just 13x10cm PCB size!

Now AVR runs BASIC, TURBO PASCAL, C, FORTRAN etc., plays TETRIS and other games, makes text processing, runs spreadsheets and much more. CP/M software world is much wider than it is usually imagined and CRISS can "switch" the platform on the fly without rebooting!

All videos are from the real device, no emulation! :)

As a component base the line of the Microchip (Atmel) AVR family was chosen as a reliable and honest 8-bit platform. All interfaces are implemented using specialized microcircuits. Internal frequency is 20 MHz, Z80 emulation corresponds to the 4MHz z80 CPU, 1us register-to-register operation time.

The computer is built following the classic structure: the central processor is implemented using the ATMEGA1284P and emulates Z80 CPU with extended commands set, the peripheral controller is built on the ATMEGA328P, the VGA controller is built on the ATMEGA328P and ATTINY13 without overclocking(!), the Ethernet controller is ENC28J60 (Microchip), RTC is DS1305 (Dallas), the RAM 64Kx8 is W24512 (Winbond) but 128kB chips also can be used. 

Internal SPI bus with the address decoder allows easily add additional peripheral device: CAN bus etc, such devices are accessible via IN/OUT commands from the user programs in any language.

100% open project, send me requests for any info, DIY kits and assembled boxes are also available!


Schematic and wiring diagram

Portable Network Graphics (PNG) - 233.07 kB - 08/29/2021 at 08:01



PCB layout

Adobe Portable Document Format - 41.55 kB - 08/25/2021 at 15:48


Firmware level 0: bootloaders

x-zip-compressed - 2.98 kB - 08/29/2021 at 07:54


  • 1 × ATMEGA1284P Microprocessors, Microcontrollers, DSPs / Microcontrollers (MCUs)
  • 2 × ATMEGA328P Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × ATTINY13 Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × W24512 Memory ICs / Static RAM (SRAM)
  • 1 × ENC28J60 Ethernet SPI adapter

View all 7 components

View all 4 project logs

  • 1
    Video-lesson for home assembling

View all instructions

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esiako wrote 4 days ago point

nice but how long this device work on one AA?

  Are you sure? yes | no

Igor wrote a day ago point

Good question! Not so much in the current version. But it can be split into 2 parts: main CPU controlling external device via UART and the "rest": VGA, SD, ... to control and setup it. In this case you will be able to program it using any programming language and standard keyboard/monitor, save the program to the EEPROM and CPU will execute it without unnecessary "extension". Firmware supports it. In this case you can either consider low-power RAM or use "sleep" feature of the firmware, that puts computer into power-save mode for desired interval. In such architecture AA can be really considered as backup power source.

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aldolo wrote 10/09/2021 at 02:40 point

nice and clean assembly. as usual software is more valuable then hardware if cp/m is still a thing. thinking about the dotmatrix printer in the attic...

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Igor wrote 10/09/2021 at 07:39 point

You can revitalize it with the CRISS CP/M! :) Serial printers are supported "from the box", for the LPT support you'll need just tiny converter board that fits into the DB25 socket.

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Igor wrote 10/06/2021 at 11:09 point

Wow! Minesweeper for CRISS CP/M was included into the official list of Minesweeper games! Take a look at here:

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xyzzywny wrote 09/01/2021 at 23:27 point

where are the applications shown in the video available?

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Igor wrote 09/02/2021 at 05:02 point

Take a look at Support - Soft. Thanks!

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Hakaday wrote 09/01/2021 at 18:48 point

Cool retro computer!

Please do take into consideration for your own safety when a PCB has both mains and low voltages.

  Are you sure? yes | no

Igor wrote 09/01/2021 at 19:42 point

Thank you for the comment! Yes, it is considered and the magazine article contains exact instructions how to be safe and isolate high and low voltage sides. The PCB also has an option to use external 5 VDC PSU instead of 230 VAC. During the design time only 5V power must be used, there is special connector for that near the LAN socket. Thanks!

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