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Multicomp FPGA Retrocomputer Builds[edit]





EP2C5-DB FPGA[edit]

EP2C5-DB RevX6 720px-rot.png

Grant Searle's FPGA MultiComputer Project(s)[edit]

Retro-Computer Map EP2 to EP4 card[edit]

  • Map EP2 to EP4 card

My Build of the Z80 Version[edit]


Retrobrew Computer Builds of the Multicomp Project(s)[edit]

Neil Crook Builds of the Multicomp Project - 6809 Version[edit]

Neil started from Grant Searle's work and fixed a number of issue with the VHDL code.

CP/M Resources on the Net[edit]

CP/M Notes[edit]

  • CP/M is not case sensitive
  • REN NEWNAME.EXT=OLDNAME.EXT - Rename a file from the old to the new name
  • ERA FILE2ERA.EXT - Erase a file
  • Asterisk is wildcard
  • .COM are command files
  • PIP - copy command
  • Drive references A:
    • Drives go from A-???
  • LS is a better direction program

Microsoft BASIC Notes[edit]

  • SYSTEM -- Return to CP/M
  • NEW - Delete program
  • OUT 132,1 -- Output to I/O port 132
  • PRINT MEM - Free memory (6809 Extended BASIC)


  • Grant noted about the SD card interface:
... the SD controller is easy to control - in BASIC POKE the sector number, POKE the write command, 
POKE 512 bytes to the same location to write a sector, 
or POKE the sector number, POKE the read command, and PEEK 512 bytes to read a sector.


Z80 P865-cropped-720px.jpg

Our Retro-Computer Projects[edit]

  • Land Boards EP2C5-DB FPGA Retro-Computer card
    • Duplicates Grant Searle's design down to the pin maps
  • Land Boards BASE-EP4CE6 card is a breakout board that connects via cables to the Land Boards EP2C5-DB card
    • The Land Boards EP2C5-DB card adds extra logic and RAM resources beyond the EP2C5 FPGA
      • Provides 16K of Internal SRAM
    • Wiring is here
  • Purchased EP4 FPGA card
    • Includes VGA, PS/2 and USB-Serial converter
    • Other I/O is serious limitation but a 16K retro machine without SD Card storage can easily be built
  • Land Boards RETRO-EP4
  • Land Boards RETRO-EP4CE15

Our Retro-Computer Video Series[edit]

EP2 Video Series[edit]

Video Series

EP4 Video Series[edit]

S120 Bus Computer[edit]

Back in 1977 (before my Ohio Scientific SuperBoard II I had my own homebrew computer. I never took any pictures of it and the hardware is long gone now. These are the pieces of it I remember.

  • Ran on Elco? 120 pin edge connector cards
  • 6800 Processor board running at 1 MHz
  • 2K of Static RAM board
  • 2716 EEPROM board (may have had 4 sockets total, don't recall for sure)
  • Front panel switches and LEDs to enter the address/data (Step/Insert) and blink lights

I remember getting it to run and I do remember blinking a light back and forth on it. Once I got the SuperBoard II, I stopped working on my own board.

It might be fun to reproduce that board!

Pieces to Reproduce my original S120 Bus Computer[edit]

  • Michael Holley's SWTPC 6800/6809 documentation collection
  • N8VEM RetroComputing Wikipedia page
  • Retrobrew Computers
  • Kim-1 board - Similar concept


  • M6800 VHDL code from OpenCores


  • AS68 Cross Assembler
  • ASM68C Cross Assembler
  • Collection of Assembly Language tools for the M6800
  • 6800 Basics
  • 6800 Assembly Language Programming (pdf) by Lance Leventhal
  • 6800 Instruction Set Cheat Sheet

Ohio Scientific SuperBoard II - My first commercial personal computer[edit]


SuperBoard II

  • Manufacturer: Ohio Scientific
    • Model 600 Rev B Board Manual
  • Model: Superboard II ( Model 600 )
  • Available: 1978
  • Price: US $279 assembled
  • CPU: 6502
  • RAM: 4K static RAM, 8K max
  • CEGMON - Monitor in 4K of EPROM
  • Display: composite video, 30 X 30 text
  • Built-in keyboard
  • Single board design
    • I eventually got a RAM expansion card with Floppy Disk Controller
  • Ports: composite video, cassette
  • Storage: cassette
  • Microsoft BASIC
  • 2K Monitor ROM (CEGMON)
  • Compkit 101 - British clone of the SuperBoard II

Superboard II Documents[edit]

CC65 - C Compiler for the 6502 and OSI C1P[edit]

SuperBoard II Emulator[edit]

BASIC Programs[edit]

10 I=1
30 I=I+1
40 IF I < 5 GOTO 20

SuperBoard II/ Retro-Tech Refresh[edit]

I was looking around for a way to recreate my OSI Superboard and found Grant Searle's design.

  • EP2C5-DB - Our creation of a daughtercard which implements Grant Searle's Multi-Computer
  • CompuKit UK101
    • Based on Cyclone II EP2C5 Mini Dev Board
    • Someone built one of the CompuKit clones as a CPM box
  • Compukit 101 video

6502 Computer Projects[edit]


DEC (Digital Equipment Corp) Computers[edit]

External Sites[edit]

Grant Searle Terminal Design[edit]

  • Uses two Arduino'ish processors to implement an entire terminal
    • NTSC output
    • PS/2 Keyboard input
  • Grant Searle's Monitor Keyboard Design

ATMega328Video 2.2.gif

  • Older AtMEGA32 version of Monitor Keyboard Design
  • My implementation of Grant's small serial terminal design.


RetroBrew Computers Site[edit]