How to Turn your ESQ-1 into an SQ-80

by Rainer Buchty, edited by Noah Vawter

Disclaimer: If you're crazy enough to try this, you're probably in a home somewhere, so you don't have any ability to sue! ha hah aha

Main Differences

The ESQ-1 is similar to its big brother SQ80, it just lacks the floppy drive/controller and mapper (single D-type flipflop) which switches between DOSRAM and SEQRAM. Also it comes with only 8kB of SEQRAM but easily can be expanded to 64kB of SEQRAM.


From the OS's point of view they are almost identical, I had a quick look inside ESQ-1 OS V3.5 and recognized almost all routines I knew from the SQ80 OS V1.8.


  • Attach the FDC (1772, needs another 74139 for address decoding, the E-clock based read and write signals should be ready since the cartridge is driven by these) and a shugart-compatible 3.5" floppy drive (any PC drive should work),

  • Implement the mapper (another 74139) and DOSRAM (6264),

  • Plug in more SEQRAM (two 62256)

  • Exchange the WAVEROMs (two 27512) and OSROMs (two 27256) by the SQ80 versions. If I'm right this should be all necessary steps to turn a ESQ-1 into an SQ80.