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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 - Our 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
  • Ports: video, cassette
  • Storage: cassette
  • OS: Microsoft BASIC in ROM machine "monitor"

SuperBoard II/ Retro-Tech Refresh

Superboard II Documents

BASIC Programs

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

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

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(s)

  • Neil did work on the 6809 core that Grant Searle was using
    • Changed reset to active-low, consistently asynchronous
    • Changed clock to rising-edge
    • Clocked the processor on the input (50MHz) clock rather than a divided clock
      • Used the HOLD input to control the clock rate.
    • Added MMU to control extended RAM
  • Neil did some Video Display Unit (VDU) Modifications
  • Neil's Memory Mapper
  • Neil got SDHC working - the original was SD only

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