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S120 Bus Computer

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



Ohio Scientific SuperBoard II - My first commercial personal computer


SuperBoard II

  • Manufacturer: Ohio Scientific
  • Model: Superboard II ( Model 600 )
  • Available: 1978
  • Price: US $279 assembled
  • CPU: 6502
  • RAM: 4K static RAM, 8K max
  • 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

CC65 - C Compiler for the 6502 and OSI C1P

SuperBoard II Emulator

BASIC Programs

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

SuperBoard II/ Retro-Tech Refresh

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

Our Retro-Computer Video Series

We have tried to get Grant Searle to arrange something with us. I want to figure out how to give him some money from selling the cards before I put them up for sale. We posted on his Twitter feed with the hope of starting a conversation about this. No response so far. Please don't email me asking me to sell you a board.

Video Series

6502 Computer Projects

Other FPGA Computers

Robert Baruch's Series on building an FPGA Computer from scratch

A machine to Run Zork

Grant Searle's FPGA MultiComputer Project(s)

My Build of the Z80 Version


Retrobrew Computer Builds of the Multicomp Project(s)

Neil Crook Builds of the Multicomp Project - 6809 Version

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

CP/M Resources on the Net

CP/M Notes

  • 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

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

DEC (Digital Equipment Corp) Computers

External Sites

Grant Searle Terminal Design



RetroBrew Computers Site